I've done quite a bit of video editing, and I have the 7D.
I have used Premire Pro CS3 with the 7D
I have used Sony Vegas Pro 8 & 9 with the 7D
I'm going to reccomend straight up: Sony Vegas Pro 9.
I think it's great, very responsive, great built in effects, great sound managment... great everything!
Premiere Pro is good too, but I just don't think its as responsive and intuitive as Vegas.
One thing I will mention is you will need to TRANSCODE THE MOV. FILES FROM THE CAMERA.
The files are hefty, and editing the raw files is difficult even for top end computers.
You can reder all your footage to avi. or something with the codec's built in to the software...
oooor, the best option, buy a good codec (like Cineform Neocene) then transcode to avi. that way.
The quality will be great, and playback will be smooth.
I've made a few short films with the 7D and although it's quite hard to handle, it has the potential to blow a lot of dedicated video cameras out the water.
Good luck!
EDIT: Okay you have CS4, do you have a recent version of quicktime? Software needs the quicktime plugin to support the mov. files... just install quicktime as normal, reboot and it should sort itself out.