Well that's a loaded question.
The G4 processor is better than the Athlon MP when it comes to video editing because of the shorter pipeline. The Mac OS X is also much better at audio than anything microsoft has out. Debian Linux is hoping to create a low latency operating system, but it has yet to surface. BeOS is the best audio operating system out there and has the lowest latency of any operating system.
G4 solution:
Final Cut Pro 2.0 is the standard for Mac and it sucks at audio and still has major issues with it as does OS X. Adobe Premiere will work on a Mac, but if you are using Premiere then use the Athlon MP platform cuz it's cheaper for all of the hardware.
The Apple hardware platform has only 2 good cards (depending on how much you have to spend) the RTmac from Matrox and Pinnacle Cinéwave.
Athlon Mp solution:
Athlon MP on the other hand can use winNT, win2000, Debian Linux, or BeOS.
Athlon MP can use tons of hardware and software (anything Discreet, Avid, Speed Razor, Boris, Pinnacle, Matrox, Targa, etc...)
To get real time effects on your Athlon MP you can either:
Run BeOS as your operating system and have Personal Studio for your NLE. That solution does not require you to purchase a real time card and can run 10 layers in real time effects. The downside to BeOS is it's lack of support for expensive high level NLE stuff.
Run winNT or win2000 with a real time card such as Matrox rt-2000. That solution can only run 2 video layers and one text layer in real time, and the card alone costs $999.
Some great sites are:
http://www.promax.com/ and
http://desktopvideo.about.com/?once=true& .
They even have an article on your particular issue:
http://desktopvideo.about.com/library/weekly/aabyb_nle.htm