It would be interesting to hear if someone can clarify something for me.

Let's say that as we wander through our videos in post the computer needs to calculate each change to the image frame by frame.

So, if the camera is sationary, is it possible that the computer has to do less work, and therefore needs to be less powerful? Conversly if every frame is different the comp has a harder job?

Or does the system simply recaculate every frame every time irrespective of content?

Also bear in mind that any effects added to the clip have to be calulated also, so if your footage is raw it'll demand less than effected stuff, that I do know about as it was perfectly evident when I was editing on this machine.

Edit: Btw I've also found advanatges in using a machine dedicated to video editing. This helps by running a minimal system, as any amount of memory resident clutter helps to jam things up otherwise.

I forgot to mention, my dad uses that computer for audio production. Maybe thats the problem I'm having troubles with Premiere ? .....
Because when I'm installing Premiere, it reads all the audio plugins on the PC ......

I dont think that will cause any problems, many sound plug ins are designed to be used by many programs including many video editors.

Which version of Premiere are you using I found with Premiere 6, I always had to check the project settings if I ever change the export video from DV avi to mpg and back again, it would always default back to NTSC for some reason, so I got in the habit of always going into project settings to make sure things hadn't changed and checked that it was DV avi PAL, I also made a preset up that was "lower field first" "interleave 1 frame" "no re-compression". I found that if I left the interleave at the default setting the audio would go out of sync after about 5 mins. with the interleave at 1 frame I had no problems.