Go with TheBeets suggestion. That's a good list of free stuff.
WMP is a bit of an oddball with what it will play, what it needs etc.
It doesn't take much to stop it working and it's a devil of a job to fix.
I suspect that a few of the "essential" codecs have been deleted when you removed some programs during the re-install (some remove stuff, shared or not).
Have you tried a fresh download of WMP from Microsoft? I think there is a codec bundle you can download as well.
Oh, one question, is it just one particular DVD or all DVDs and, if just one, is it a bought or home-burnt one?
Finally, try the Microsoft support groups forum. They are pretty good at fixing things and have some genuine Microsoft experts and VIPs there.
It's a devil to find but I bookmarked it
http://www.microsoft.com/communities/newsgroups/en-us/default.aspxthen use the table at the side to navigate to what you want (English, Windows, Windows XP,Media Player etc) - I have found them more than helpful on several occasions when something went wonky
