Choppy video playback on windows 7

Windows 7 is usually very smooth and easy to work with so something else maybe going on.
Possible causes: Low power CPU. Low installed amount of RAM. Unusually high number of programs/processes already running. Possibly incorrect video driver.

Most probable reasons:
[1] slow cpu
[2] slow graphic card
[3] inadequate RAM

Does your pc satisly the min reqs of Win 7 32/64 bit OS?

Make sure your video drivers are up-to-date... it sounds almost like they've been corrupted or even uninstalled.

Open up device manager and check the properties of your disk drives to make sure they're running in DMA mode and not PIO mode.