supermep

It's probably being used.

Open up your task manager and close basically everything in there besides:

SVCHOST.exe (there will be about 8 of these)
SYSTEM
System Idle Process
CSRSS.exe (if you have it)
Services.exe
Spoolsv.exe

Then attempt to delete it. If it STILL does not delete then you might have to stop a service.

Hijackthis is also a great program to attempt to delete it with.