This was posted by Daniel Cziranku on another site.
After trying it out, I found it worked fantastic, and want to share it here.
Here is what he posted.
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If you use Windows 7, and you have a strong machine but still have some LAG, low FPS or unstable performance, here's a little trick you can try:
You'll have to turn off Multimedia Class Scheduler in both msconfig, and modify a key in the registry. This module causes fps drop-down, lag, and many more terrible things to our gaming performace. I turn this off on every build of Windows 7, every install.
so, let's get started

STEP #1
1. click on windows key / start menu
2. in the search field type and run: msconfig
3. click on the services tab, and search "multimedia class scheduler". uncheck the checkbox
4. if unchecked, click ok. when asked, DON'T restart your system. do STEP #2 before restarting !
( also, you can go through the "startup" tab's list, If you have something that isn't necessary to start with windows bootup, you can take them out easily here. this can save boot time and memory, too )

STEP #2
1. click on windows key / start menu
2. in the search field type and run: regedit
3. on the left side open the following path: HKEY_LOCAL_MACHINE > SYSTEM > CurrentControlSet > services > AudioSrv
4. click on AudioSrv, and on the right side of the window there will be a list, search and doubleclick "DependOnService"
5. after you opened the little window, DELETE the "MMCSS" part. only that part, leave the other 2 alone.
6. if you deleted it, click OK and restart your computer.

ACHTUNG ! you need to go through both step 1 and step 2 in order to fully disable this little imp !
I gladly help anyone who needs it, just drop some letters and I'll reply.

Hope it helps a lot of you, have a nice day !