do i need to run MsMpeng.exe which is some sort of spyware built into windows even if i have got other spyware running.
because it seems to slow down my computer by useing a lot of my cpu by alot i mean 65% constantly

It is not spyware, but part of Windows Defender, a Microsoft anti-spyware application - it is NOT built into Windows. Are you using OneCare? Does it consume lots of resources all the time, or just every once in awhile. You might want to check when it is running it's scheduled scans, and possibly reschedule scans to the middle of the night, or some other off-peak hour.

thanks for the advice i changed the time it scans to the night like you sugested

Hopefully it will not interfere with your other computing activities.