...which makes it impossible to play games or do other stuff...
look at this 2 pics:

Cpu usage ~50%

Cpu usage ~6%
when i restart my computer everything is okay it only happens sometimes....
EDIT: Btw when i play games it runs 1 sec smooth and then it stops 1 sec and so on -_____-
Does anyone know anything about it?

Thank you

older AMD X2/opteron core? try the dual core optimizer. http://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_871_9706,00.html

nope but thank you
my sys-stats:
win xp sp2
intel core 2 dou e6850
4gb ram
geforce 8800GT 1024mb

Quite logical question - do you have antivirus installed and does it match the latest update?

I have avira antivir (the annoying free version) and zone alarm.
Avira has always the latest updates and zone alarm shouldnt be a problem since a lot of my friends use it and they haven't got this problem.
I think it should be someething else since this problem shows up every 15 times (or whatever :-D ) i start my computer

Try to switch the antivir software off and disconnect from Internet.

Besides that search for Spy tools. Today the real threats are no virus-infections, spy tools are worse. I had the same problem in the past and only SpyBot S&D could help me:
http://www.safer-networking.org/de/index.html

It is free but I donated some money after this because they saved me.

Okay i will try that when i have this problem next time.
But i think it cantbe spyware because i already had this problem before i reinstalled windows

Or try CureIt! (free util to scan pc from viruses & delete them).
http://www.freedrweb.com/cureit/
It will find all variety of dangerous\potentialy dangerous content (even adware).

and you have an incredibly long process list. why did you cut it off at the left side?

You should also probably do a rootkit scan. Try Rootkit Hook Analyzer an RootkitRevealer