You might want to look into Kavoom as well. I've been using it every since I went to three computers and I like it. Easy to use and setup. You can also download and install it for free to try it out. I think there's like a 30 minute time limit or something like that, but it was enough to convince me to buy it.

Kavoom KM lets you move the mouse between multiple computers. Kavoom KVM lets you type directly on different computers from the one keyboard. You'll need that to work on macros and various other things that require keyboard input in WoW on the second computer.

I recommend it over all the other options that I tried to figure out with no success when I was setting mine up. I'd rather spend my time playing and figuring out other stuff. Never heard of Interbox from the other poster, but I'd like to hear about your results if you try it.

www.kavoom.biz