Hi Kate. I do not use Win Media player for burning...there are better alternatives.....In Fact I do not use that media player period. There are better freebies that are more user friendly and do not want to take over your PC. I would not attempt to burn a disc with any other program open as this can cause conflict probs and ruin the burn.

I am still not sure what you are doing.....Vista and 7 are two completely diff op systems. I am not sure how you can use both at the same time...perhaps you upgraded to 7.....in which case Vista would have been blown away first.

The probs you are having may be down to running a 64 bit system with Audacity which works on 32. Here is an article explaining about this prob.
http://wiki.audacityteam.org/index.php?title=Windows_Vista_OS
I also would suggest now that you do use the 1.3 beta version of Audacity contrary to what I said before......I was assuming that you had XP or Vista and were running a 32 bit system.
If you are running the older version of Audacity this could be the cause of the probs. You may have to install special drivers if you have further probs.