VLC media player does not support windows vista right out of the box. You need to tweak it in order to get it to display the video. Here is a how-to on configuring VLC on a Vista.
1) Open VLC.
2) Press CTRL + S to open a preferences box like one shown below.
3) Click on the Video options from the tree.Check the Advanced options check box present at the lower bottom of the preference box.
4) This will enable a video preference option box like one shown below.
5) Now, click on the Plus sign next to the Video option. It will give a detailed menu. Select Output Modules from the list. It will give the following options.
6) Now, Select DirectX video Output function and save the settings by pressing ALT+S. Next, try to play a video and see if it is working fine or not. If not then follow the next step.
7) Else, select Windows GDI Video Output module and it should work fine.
Well if you are unlucky with both the options then the last resort will be to select Dummy video output function.