Step 1:
Connect your computer directly to the modem. Set it to use dhcp on the wired interface.
Press "Renew dhcp lease" and tell us what you get.
If you don't get anything or an address like 169.254.xxx.xxx then dhcp is not working. If so try entering what you beleive is right.

If you got connected.
Step 2:
Reconnect the linksys. Connect your computer with cable to the linksys and see if it works.
Test with both the number you have and enter them manually. Then test with DHCP.
Try to open http://72.14.207.99

Then tell us the results of these tests and exactly which numbers you entered or got via dhcp.

I was able to get the computer to access the Internet when I connected it directly to the modem and enabled DHCP.

I then connected it to the router. I could not get the computer to access the Internet with DHCP. Instead, I used the following in Network settings to get the Internet to work again:

Configure: Manually
IP Address: 192.168.200.102
Subnet Mask: 255.255.255.0
Router: 192.168.200.1
DNS Server: 192.168.200.1

192.168.200.1 is the address assigned to the router.

What insight does this offer for how the Airport Express should be configured to allow access to the Internet?

I'm really stuck here. I've done what people have suggested and still don't know what to try to get my Airport base station working again.

What do people think will fix this problem?

I still have not been able to fix the problem with my Airport Express base station. I am posting again to see if anyone can come up with some solution.

Here is what is going on:

I have home network that consists of a DSL modem connected to a Cisco Linksys router. I have two desktop system that are connected to that router. They can both access the Internet just fine. Both system are set with manually assigned IP address from my private network.

Up until recently I also had my Airport Express connected to the router and that provided a wireless connection to the Internet for my iBook, which I also manually assigned an IP address on the network.

Everything was working great, until one day I received and notice there was an update for the Airport base station. I installed the update, and since then I can not get the Airport Express working properly.

I can reset the base station, hook it directly to the DSL modem, set up a wireless network, and everything is fine for the laptop. This of course prevents the Linksys router and the two systems attached to it from accessing the Internet.

If I connect the base station to the Linksys router, and set it to bridge mode, it will continue to flash amber. Thus I cannot access anything from the laptop when the other two systems and the Linksys router have Internet connectivity.

If I keep the base station in bridge mode and assign a manual IP address to the base station that is similar to the addresses I've given to my computer systems, then the base station will display a green light. I can use the iBook to access the other computers on the network. However, it still cannot access the Internet.

What can I try that will get my wireless network working properly again?

First off, you need to distinguish between being able to access the Internet and being able to access web servers etc by name.

As a test, try accessing some web site by IP address instead of by name to check if your problem is merely a DNS problem (where you do have Internet access but your computer doesn't know how to translate from the names (e.g. www.apple.com) that you give it and the IP addresses that it actually uses).

To do that test, first find out what the IP address of some site (e.g. www.apple.com) is by running one of the following commands on a Mac that is working properly:

host www.apple.com
OR
ping www.apple.com

Then use that IP address instead of the name on the Mac that isn't working properly. Does it work with the IP address? If so, you have a DNS problem.

Neither pinging by name or IP address work. However, they fail in different ways. Here are the results of trying to ping Google:

ping www.google.com

Ping has started ...

ping: cannot resolve www.google.com: Unknown host

ping 209.85.171.103

Ping has started ...

PING (209.85.171.103): 56 data bytes

--- 209.85.171.103 ping statistics ---
5 packets transmitted, 0 packets received, 100% packet loss

What do these results indicate?

The second result (ping with an IP address) is more important. It indicates that although your Mac "thinks" that it can send packets to that address, nothing is getting through - or maybe it's getting through but nothing is getting back.

Hard to diagnose these things from a distance. You need to eliminate each variable in turn by trying different things.
- try a different Ethernet cable (between the Airport base station and the router - and maybe other places that you can think of ?)
- try your Mac via an Airport (wireless) connection at some other location - i.e. someone else's wireless network - e.g. a friend's, an Apple Store, a Starbucks, etc.
- try a different Airport basestation connected to your router (e.g. borrow a friend's, etc - might be difficult to arrange I know)

Looking back at your previous posts I see that it worked fine if you connect the Airport base station to the modem directly. So maybe the problem is with the router or its configuration (some routers have a weird setting that isolates the wireless and wired networks). So try a different router or just look around in the config of the router.

I'm pretty sure the Ethernet cable is fine as I attach it to the iBook when I need to use it on the Internet.
I've had my iBook at a coffee shop lately and was able to access the Internet there.
I don't know anyone that has another Airport Express.

It seems that maybe the Airport Express is damaged, and won't work properly with the router. I don't know if I should consider replacing it.

Don't neglect the possibility (as pointed out above) that the problem is with your router or its configuration.

As far as I know, nothing has changed for the Linksys router. It is using the same configuration it always was when the Airport base station was working fine.

It is a Etherfast Cable/DSL Router with 4-port switch, Model BEFSR41
What things should I check or change in the Linksys configuration?

I realized that when I connected to my wireless network after resetting by base station, that the system had changed some of my network settings. I reset it to assign an IP address manually, and specified the Linksys router as the router.

After doing this, I can ping www.google.com by IP address. I still cannot ping it by name.

So, it looks like I might have a DNS problem. What should I do to troubleshoot this issue?

You could put the addresses of the DNS servers that your ISP told you to use in the Network preferences on your Mac

I set the DNS server to my Linksys router in the network settings for the iBook and now it is resolving by name.

Thanks for your help.

I agree. I also have westsell and use verizon dsl. It is ppoe but I dont have a problem accessing net with my MBP, but seeing other computers is prob. If I understand that is also your problem? Yeah I can use either Dynamic pr PPoE, but I pull in net fine. In fact I can access the mac from my windows desktops, but the mac is blind.

My problems are resolved now. My wireless network is working like it did before the Airport update screwed everything up. I'm not sure what your problem is.