Windows Media Player. VCD is just a MPEG stream. You can watch the movie by just opening up then AVSEQ0x.dat file in Windows Media Player.
If you don't like that, try QuickVCD. It's something simple I've used on occasion.
If it's an SVCD, you'll need an MPEG2 decoder that comes with software DVD players. I personally use PowerDVD to play all my VCDs, SVCDs and DVDs, but that costs money (it was bundled with my DVD drive though!)