Got fed up with Microsoft Media Player 9 and went and bought a copy of PowerDVD v5. Purchased the standard version and downloaded direct from Cyberlink (for immediate gratification!). Was having codec problems with media player as it wasn't playing the ISO images of some DVD movies I had and just locking up. PowerDVD played them perfectly.
I did do a quick bit of research beforehand as the choice was between WinDVD and PowerDVD. PowerDVD seems to be the more popular choice but there's really very little to differentiate them. WinDVD sells too many addon's while PowerDVD bundles it all together. Got the standard version because I don't have surround sound (sob!) or any need for DivX support.