I am getting sick of this... There should be a separate read-only bugs forum containing important threads copied from other forums. Most people don't understand the difference between 'bug repots forum' and 'tech support forum'.
... and about mmsystem004 - look here: http://forums.winamp.com/ubb/Forum13/HTML/000797.html
Also MAKE SURE that there are no other programs using your sound card. If you have SBlive, go to AudioHQ / device controls and set higher maximum simultaneous Wave playback.