I think I might be able to help you with that. Im a student from Los Angeles Film School and we edit HD as well as Standard Def, 35mm, and 16mm...no flatbeds, or macs, just pc's.

We edit on Avid. But hardware wise...especially dealing with HD. Hardware is most important.

You're definitely going to need atleast 2 processors to do the job. Currently, before I left, we were using 2 xeon's running at 3.2ghz. with 2gb's of ram. Your current processor won't be able to handle such a load. Dual cores are the thing especially for rendering. And my athlon 4200 does the job. But probably not for hd.

So let me tell you what Im getting for my rig. (Hopefully one day). I alrerady have half the parts...

2 Opteron 285's.
Tyan two processor, dual core motherboard
4gb's of ram corsair xms pc3200
2 74gb western digital raptors raid 1
1tb of system storage
1tb g-tech external hard drive
(soundcard your preference)

Avid Xpress Studio Bundle w/ mojo
and to keep the camera from wearing out...

An hdv recorder...
Sony HVR-M10U


hopefully that helps out a little bit. =)