The iMac isn't online at the moment because I haven't needed it to be until now. It's been on my list of things to do for a while now, but it keeps getting bumped lower and lower by other, more urgent things (computer related and not). Thanks for the suggestions for the wireless-B and USB adapter, one of those would be the most practical option.

Edit - In my dream world all of the computers in my house (both the modern ones and the vintage ones) would be connected to a network that would allow them to transfer files between them without SneakerNet, as well as access the internet. I still can't directly transfer files between my Windows 7 computer and a family member's Windows 7 computer, I've had to use email or SneakerNet. Networks appear to hate me, and lately (since I've needed to transfer a bunch of large files) the feeling's been mutual.