I've got Vista on a PC, and as you've observed, very little works.

On codecs - what format are the files you're trying to play? From what you say, I reckon if you go to DivX.com you'll find what you're after.

On the installations, do you get errors? have you checked the eventlogs? If you can give me more info, I might be able to offer some advice.

It's no help to you now Spider, so I apologise for saying it, but Vista is just a nightmare and it's not worth using until MS have put out at least 1 service pack...