no playback at all in Windows XP PRO x64
then i turn off audio input in ASIO (audio hardware) now i can playback without any problems.
Windows XP PRO x64 sp2
Premiere Pro CS4 v4.1
1 - make sure compatibility is set to 32bits
2 - always run as Administrator
3 - make sure you have the latest sound drivers
Otherwise, I'm not aware that PPro was ever certified for Xp64bit (which is sort of a sideways step for Microsoft, and from what I've read, very little was actually written for or tested against that version)
Upgrade to Win 7 64.
John is correct - Premiere Pro CS4 is not certified to run on WinXP64. However, I would try a lot of things before switching the OS (unless it's convenient). XP64 does work for many people - Adobe just doesn't officially support it.