VNC from Windows gives blank login screen
VNC server changed on lion. You can now log in without a vnc password but instead he os users each get their own loginwindow allowing simultaneous log in distinct from what the local display shows. 

Some discussions on what exactly changed can be found here: Are the changes to Lion&#39;s screen sharing documented anywhere publicly? 

I do know the mac screen sharing client as well as edovia's iOS screens apps work well with the new lion changes, so there's hope other third party clients can get updated to work better with the new changes.