Run a really really long USB cable.
AIM has it built in. Yahoo messenger. Netmeeting. Set up a website.
I'd suggest net meeting. It can be hacked, but 1) who's going to hack you? and 2) who cares if a random hacker catcher your baby sleeping.
Id set the baby's computer to auto accept calls and auto broadcast video. That way you can "call" on your computer hwen you need to take a peek.
The other route is an ethernet camera accessable from any networked computer. There are much better quality but a bit pricey.