I think your earler post stated that you were running Vista. This is from the Winamp FAQ's
Is Windows Vista supported?
Yes, but there are currently a few known issues that the development team are working on. DirectSound hardware acceleration no longer exists on Vista (resulting in potentially broken support for 5.1/7.1 speakers); Skinned scrollbars may not be displayed correctly; Video playback may be a bit flaky (most likely related to old/buggy video drivers or DirectShow codecs) or doesn't work at all with Aero enabled; and DWM/Flip3D displays the built-in Classic skin for all Modern skins (note, you can enable support by setting vista_thumbnail=1 in winamp.ini, but it still won't work when Winamp is minimized). We hope to resolve most if not all of these issues in forthcoming Winamp releases.
So it may be related to on of these.
I would add that after 18 months to not be fully compatible is really totally unacceptable. If there was only the free version there would be no room for complaint, but there is also the paid for Pro version.
The fault here lies fully with Winamp and not Vista.