Hey there antiquerose
Try double_a_ron steps first and see if they help, I personally don't have much experience with the All-in-One codec pack, but if double_a_ron recommends it then it must be good.
Codecs are a major headache as you are finding out..
I recommend you do the following:
So after uninstalling the codecs, reboot your machine and install the K-lite pack, during installation I want you to scroll down the list of "custom selection" and enable
mpeg demuxer and anything under the
dvd decoder.
Once this has finished restart your computer and see if you can play your files properly.
DVD problems
This is going to be an issue, there aren't any 'free' codecs out there that allow you to play DVD's through WMP (not that I can find anyway

)
There are a whole lot of the market:
- The DVD XPack
- Cyberlink
- Intervideo
http://www.microsoft.com/windowsxp/u...02april15.mspx
Normally DVD drives come with Cyberlink Power DVD, did you get one of these disks?