Will any of the switches handle a PC keyboard and mouse with an Apple Desktop Buss? Monitor will be no problem since we are already using a PC monitor and an adapter with the Mac. It is a Power Mac 6600 running Mac 7.6. We need to share an ethernet connection too.

I'm not sure about the KVM, but for the ethernet connection, you'd probably be better off with a switch or a hub. If you get one that supports either Uplink or Auto MDI/MDI-X should be able to connect to both computers and another router/switch/hub without having to use any special cables. If you have one that doesn't support that, you could connect it to your existing network with a crossover cable.

I'd rather just connect both of them to the network at the same time, rather than mess with finding a KVM that supports PC/MAC hardware AND a network connection. Besides, that way you can still connect to one on the network even while you're not controlling it.

If you don't have a network set up yet, and you need to just share an internet connection, you can get a router for a decent price to keep both of them online. Usually they're about $30 for a cheap one if you look through the paper and find one on sale. I'd recommend and Linksys or Netgear (people like D-link too, but I've never had good luck with them)