I put in the public WAN from the ABS, which then forwards to the port on the G4. (I obviously can't use the manually assigned IP, as it's only an address for my LAN (10.0.1.101)

Yup, yup, yup, and yup.

Frustrating, huh. It seems like "DIGITAL GUY" had a very similiar problem. I followed his posts and tried doing everything the same, but, no go.

Oooooh.. That's the "outside" versus "inside" I was talking about earlier. The Mac you're trying to connect from is "inside" the LAN. Are you just trying to verify that you can connect to it from the outside? First try SFTPing to it using the IP that you assigned it to make sure that it works.

True that, and I can easily connect on the network. I need to be able to connect when I'm out of town, though.

Yeah, tried it, and that totally works. Could that mean it's a problem with the ABS?

So your static Mac looks to be setup just fine. So, I guess a problem with the ABS or the forwarding setup. I don't have an ABS, I have a Netgear WiFi router, so I'm not much help on the actual setup. I'm not entirely convinced you can ACCURATELY try and access your static Mac "from the outside" when the machine you're trying to access it from is on the "inside". You might wanna take a jaunt to your nearest (shudder) Starbucks and steal some WiFi for a second to try and connect to your static Mac from a better "outside" source.

I did--SOL.

Can't figure it... doesn't seem to make sense...

OK:
Works from the "inside", sounds like the Mac is properly configured.
Doesn't work from the "outside", could be 2 things I can think of.
1) misconfigured router (your ABS).
2) your ISP doesn't allow ssh traffic in from the outside.

Seems logical--how would I find out? Call Earthlink?

Probably be easier to turn off the NAT/Firewall on the ABS/Router and test from the outside.

How do I do that?

Like I said, I don't have an ABS. I've no clue how to disable it.
You'll have to read the manual or do some googlin' to find out.

Problem Solved!!
 

After spending close to an hour and a half on IM with the generous and brilliant Robophilosopher, we got sftp (via SSH) to work. The two problems that seemed to be causing my difficulties were: 1) a wierd possibly bad installation of Pure FTPd Manager; and 2) the fact that I was trying to test it by connecting from within my LAN.

A thousand thanks again to Robo, a real resource on this site.

Cappados

Glad you got it working, no thanks to me, obviously. ;)

I'm curious what PureFTP has to do with SSH?

PureFTP didn't have anything to do with SSH. I thought it would be a simple thing to try to get FTP to work first, but cappados had installed PureFTP, in a way that seemed (I have no experience with ftpd on a mac myself) to completely change/disable the default Mac FTPd, so I was working on a lot of faulty assumptions configuring that.

As soon as we switched to getting SSH/SFTP to work, it was all fine and worked as expected.