I have been using the Screen Sharing application bundled with Mac OS X (it's in (/System/Library/CoreServices) to do all my VNC screen sharing with Windows PCs.
Since I upgraded to 10.6, every time I try to connect to a Windows PC, I just get a white screen after the password login screen.
I solved this by selecting the Screen Sharing application in the Finder, pressing Command-I, and clicking on the 'Run in 32-bit mode' checkbox. This solved all my problems; Screen Sharing now connects on the first try every time.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090916105559390