I have exactly the same problem, i'm using a 64bit-processor with winXPproSp2 and an nVidia card. vlc shows just a single-collor-filled screen instead of the video...at least i found out that it HAS to do with the skin used, because on some skins (e.g. clarity) it works fine, on some others like go! (but an older version) it doesn't. in the "Go!" skin the color that vlc shows is orange and in another skin i'm acutally creating it is a 50% grey...but i cant find that damnbug, it'll be fine if someone could help out!
PS: if it helps, my skin uses following modules:
grdtransparent-1.1_beta_1.dll
xtaskbar-1.4.1.dll
contextmenu-1.0.dll
xtray-1.0.dll
jdesk-0.73.dll
popup2-2.1.7.dll
shortcut2-2.0.2.dll
label-1.99.dll
jamptoo-1.4.dll
lsxcommand-1.9.4
gandharva-0.50.0.4.dll
xlabel-3.4.9.dll
lssliderfoo-1.8

-ZeuS-