Sony Anycast, Gobecaster? (for the life of me I can't think of the proper name or company - I think it's made by the folks formerly known as Play...), are two you might want to look at. The Sony is pretty cool. The other thing (sorry I can't remember the name) is less than US$5k, but I'm sure you have to add on to make it work. Plus it only accepts S-Video and has RCA audio inputs. Panasonic makes a little 4 input switcher, and Videonics offers a line as well. There are several other companies out there that offer solutions for this. It really depends on how much money you want to spend....
"So you want to throw out the old you - but the old you is old enough to know it won't make it better"
Del Amitri - "Make it Better"