No problem, I have the same camera, same PC, same Pr CS4 (although I'm running Windows 7 and to me it's WAY better).
Anyway, Premiere doesn't do native 5D2 format. It's a weird flavor of H.264 that Canon uses, and while Quicktime handles it well, Pr chokes.
What you need to do is invest $99 in Cineform's NeoScene:http://www.cineform.com/neoscene/
I know, I know, more money, but this one's necessary, it'll work. NeoScene is $129 on the Cineform Website, but you can get it for $99 at VideoGuys.com. In fact, I found a coupon for $10 that made it go down to $89, so hunt around for that.
NeoScene is a simple standalone program. Here's the workflow:
•Open your 5D2 .mov file in Cineform's NeoScene.
•With NeoScene, convert the 5D2 .mov file (which is 4:2:0) to an .AVI file (it'll interpolate it to 4:2:2).
•Import your .AVI into Premiere and edit to your heart's content. Pretty straightforward!
BTW, I don't even OC my i7 and it encodes in real time which is nice. However, I have 12GB of RAM, and during a simple 4-minute project, Adobe Media Encoder hit over 8GB or RAM, so while it's still cheap, get yourself more ram. I paid $80 for 6GB Patriot DDR3-1600, $55 after MIR.
In Premiere, use a 30fps HDV sequence on your timeline. Also, once you start getting your cuts together on the timeline, render them every so often so Premiere isn't overworking. Simply select the Timeline and hit the Enter key, and the rendering will begin.
I get a lot of good info in the Adobe Forums for Premiere, and some from Cinema5D.com, but those folks on there tend to be rude. On Adobe you'll find some serious video editors who know Premiere very well, but they aren't enamored by the DSLRVs like the 5D2 coming out, JSYK. So just ask your Premiere and After Effects and Encoder questions and leave out what camera you use. And if you get NeoScene, the 5D2 problem is solved anyway.
Hope this helps!