Does anyone know how you can back up a computer over the internet to an offsite drive that is hooked up to a friend's computer?

Assuming your friend’s computer is set up to share that drive over the internet, you should be able to connect to it the same way you’d connect to any remote server, using it’s IP address.

The details on setting that up and acting it out will vary depending on what OS you and your friend are using, as well as what your file transfer protocol of choice is.

Check out http://www.crashplan.com.

Either way you approach this it would be a slow process, but if I was to do this; Create a ftp server from your friends drive that’s connected to the internet. This way it works like any other website/ftp server and a big plus, you can password protect it. There are a lot of freeware solutions to do this with.