Well for that kind of stuff I would recommend a PowerMac as your main machine loaded with FinalCut Express.
I would also go for some PBs to do your presentations. The new ones WILL come very soon, so wait and get one of those.
Depending on how much money you have you can either go for a high-end G4 or a high-end G5. I'd recommend the G5, but you have to decide. Also, it's better to spend more money on the desktop (ie. RAM, HD, etc) than on the laptop so you can do all the hardcore work on it without any problems.
HOWEVER, if you do need a cheaper option and can configure your own computer, I would recommend assembling a Dual Athlon XP Box. Athlon machines are well known for doing well in video-editing and encoding. They are also known for a little less stability than the Intel boxes (which makes them a not-so-optimal choice for servers). Still, they will offer you great performance at a good price.
If you gave us a ballpark figure maybe then we can give you better advice.
Good luck,
Doc Holiday