Why is the videos in Vista so choppy?

I have Vista Ultimate. Both in RealPlayer and in Windows Media Player the videos are so damn choppy. It's like watching a slideshow in stead of a video for most videos. Surprisingly enough, only QuickTime seems to play videos well in Vista.

I have the latest, PD 3.0 build 4128. My iMac has 2GB of memory total and I give Vista 1GB of memory. Also in Windows Media Player sometimes the sound is choppy too.

 

As for video: try to disable DirectX option in Configuration-> Video

 

OK, but then won't I lose my 3D? Oh you better fix that in the next build.

 

This did NOT work at all BTW.