This behaviour appears to happen if folders are moved or renamed from that
assigned by WMP when music is ripped. This probably indicates an
obsessive-compulsive behaviour of the operator (ie you! - cant bear having
music in "various artists, various etc folders? ... sound familiar). The
solution ... rebuild the WMP database. In WMP9 this is
CurrentDatabase_59R.wmdb and in WMP10 it is CurrentDatabase_219.wmdb. Heres
how:

1. Close WMP
2.. Navigate in My Compuer (or by Searching computer) to appropriate wm
database file (above) - this should be in the folder C:\Documents and
Settings\%localuser%\Local Settings\Application Data\Microsoft\Media Player
where %localuser% is your name. Rename file by selecting the file and
hitting F2 then rename file to eg CurrentDatabase_219.old (the file could be
deleted, but renaming at this stage will allow the file to be restored if
things go awry ... but they shouldnt)
3. Start WMP and press F3 to search computer for music files.

This should fix problem of duplicates. If all seems ok, I suggest deleting
the backup to save space on comp