How do I do this?
 

What I want to do is set up it up so that two towers share an internet connection, and have file sharing abilities. I'd also really like to be able to back up from one to the other.

I want to do this using one monitor/keyboard/mouse for both towers.

Is there a way to do it without buying one of those kvm switches? And if not, is there anything specific I need to know before buying one of them?

buying a kvm won't share your interent connection. You can share the interent connection between the computers with a lan card and an RJ45 cable connected in between....
to setup the connection is easy and you can use a wizard if you got windows xp os to setup this.

you need a router for networking and internet sharing .... and belkin kvm switch to fuse 2 CPU with 1 monitor, keyboard and mouse.

I've got two routers, so that isn't a problem. I'll go check out the belkin switch.

Thanks you two! :)