Simple thing to try:
Sound control panel, select speakers (or headphones if you use them) and click properties. Then the advanced tab. Both boxes are checked for Exclusive Mode on my system and I don't have any problems, but you might try unchecking 'Give exclusive mode applications priority'.
More advanced thing to try:
Go to HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Multimedia\SystemProfile and see what the system responsiveness is set to. Ideally it should be 20, in Server by default I think it is 100. So if you are running Server that is probably your issue, if you aren't, it might still be worth looking at anyway.