Your request prompted me to do some additional experimentation (with the latest build 158).
I am using Quicktime 6.1 on two computers:
WinXP Home- Athlon 2000+- on which most quicktime files play fine under Media Center as well as as the Quicktime standalone app.
Win 2000 P3-733- on which I experience jumpy, echo-y sound when playing quicktime files through Media Center but not when playing them using the Quicktime standalone app. Is Media Center demanding too much processor time for overhead?
Interestingly, the BMW film Ambush available from
http://usa.bmwfilms.com/clap.asp?template=archive&country=usa&film=ambush will play on the Win 2000 machine under Media Center (albeit with sound problems), but not on the WinXP machine under Media Center. As I mentioned, the film plays fine on both machines using the Quicktime standalone app.
For problems experienced using Media Server see the thread "Build 157: Problems Playing Video Files". The Win 2000 machine is the server and the WinXP machine is the remote PC.
Hope this helps.