Sounds like Ed's got the answer, Martin. If you uninstall RealPlayer, be sure to do it through the "remove programs" utility on your Control Panel (assuming you're using Windows). I'd agree that you should uninstall ALL "Real" products, and then install the ones you want. Sometimes, older versions of programs that are left behind can cause big problems.
I think my sound card is quite frequently the party responsible for lockups on my computer. You'd think that sound cards would be more stable by now, but they ain't.
-Joe-