Scottysaan posted a good site and though it seems you guys have come up with a solution, I figured I would offer up some ideas for you to try.
Camfrog: I use this program and actually bought it for the full capabilities. While you're certainly not able to jam one-on-one with another guitarist in real-time, what you CAN do is have the same backing track and take turns sharing your ideas and showing what you're doing via webcam. All you need to do is set up your recording properties properly. In addition to having one-on-one sessions, there are guitar-based rooms set up that have people who frequent the rooms. When it's your turn to hop on the mic, if you have a webcam, any and everyone in the room can watch what you're doing in addition to hearing it. Naturally, the quality of audio and video depend on your connection and the connection of whoever watches/listens to you but if your connections are fast enough, the audio is one of the highest quality in any program like this. Oh, and you can send files to one another through that program.
http://www.camfrog.com
Paltalk: This is a program I used to use prior to Camfrog that's not quite as good, but it's a way for you to hop on and take turns jamming in a room of other musicians. It's a suggestion if you don't like Camfrog for some reason.
http://www.paltalk.com
Skydrive: In regards to storing files and making them available, Skydrive gives you 2GB free storage. You can sign up for an account, make files private or public and share all you want. If you want to keep some files private, you can simply create a skydrive account with a username and password that you don't mind sharing with whoever else. This completely alleviates having to worry about the troubles and bandwidth usage of an FTP.
http://skydrive.live.com
I've found the aforementioned methods fun and quite helpful. Perhaps you guys might find some use out of them as well. =)
-Stephen