I installed Vista Ultimate recently, but shouldn't wmp play mpg and such by default? I'll check if i have all codecs
Nope. ^^
Especially since some file extensions actually designate container formats that can use all kinds of different codecs.
Personally, on my quest to finding a good codec pack, I stumbled upon the XP Codec Pack, which, contrary to its name, works on all Windows systems. =)
http://www.xpcodecpack.com/
I like it because it doesn't feel bloated and has a nice site and a polished installer, which communicate to me that a lot of effort has been put into it.
I used the K-Lite codec pack before but its editions contain either too many or too few features, IMHO, without telling the user which codecs are the most likely to appear.