I doubt TCPMP can play copy protected wma files, which is why it sounds like garbage. You need to convert the files to non-protected files (which is a bit illegal) or find a player which supports protected wma.
Just found this one:
Pocket Player and though it does cost a bit it looks like it will play protected wma files.
EDIT
Bit cheaper (by $5) on
Pocketgear
Going by what is said about Pocket Player they licence the protected WMA playing abilities from Microsoft which would be why TCPMP doesn't play them, costs too much for a free application... But they also mention that for files under 32MB bookmarking a wmp audio file should work, above that there is a bug in Microsofts software which prevents it working properly.