Formats Codec Etc

I am pretty new to Kazaa etc, but have recently had my 1st dvd sucesses, identity and terminator 3. both played fine on wmp9 and burned to dvd using nero vision express.
I have now downloaded others. The Hulk, Pirates of the Caribbean and Charlies Angels 2 (don't ask... my daughters request!) ;) anyway despite the fact they have the same source (tmd) the same formats (mpeg layer 3) (ms-mpeg4 v3) they wont open in any player and wont open in Nero to burn. I downloaded k-lite codec pack which claimed to be able to convert the file but it failed to "render" and said it couldn't give me any further info.

If anybody can help me and save me the chore of downloading other versions til I hit the right one I would appreciate it.

Thanks in advance

Maverick1