What OS?
Windows, Nix or Mac?
If its windows I would go with Adobe Premier Pro, and maybe a certified boardset if you have the money.
Or check
www.pinnaclesys.com
If you want something that really kicks ass, get a Matrox boardset. Just a small one.
http://matrox.com/video/en/home/
The software runs off the boardset and that allow you to edit the video source in native format and spits it out realtime. A RT or LE board is at a Fair price now.
I recommend you spend some time on
http://forums.creativecow.net/ in their forums. Take a good look at whats there, and match it with what you need.