Is WMP able to write to CDs? - I thought it was just a player. Not an expert on this (as you can see!), but I'm using Nero and haven't noticed any conflicts with WMP (I'm running XP). I've also got Easy CD Creator installed which definately is a writing programme, and again haven't seen any conflicts. Haven't done anything special like renaming the folder.
I've had conflicts with other programs (nothing to do with this at all), which have been solved by using the EnditAll utility to close down all background programmes - freeware, you can find using Google.