What is the full iTunes path its looking in?
by default, Itunes should be:
Documents Settings/Users/Music which is the same folder (My Music) WMP looks in by default.
I think its actually a subfolder (itunes media) in the music folder, but WMP will still grab it.
To clear out WMP, Right click the empty space at the top (left of the Burn,Play,Sync Tabs) and delete the library.
Sadly, anything you add to the Windows library WMP will add to its own as well. If you want to keep those librarys intact:
to prevent WMP from adding iTunes Media, you can move the iTunes directory.
For example, make a new folder at C:/Itunes Music, and put your itunes media in it.
Open iTunes and tell it where to look for and save music, at this new location.
WMP will still add from the My Music Folder, but will not add iTunes media.
By the same token, iTunes Media will only be accessible through iTunes itself, not through Windows 7 libraries.
The other alternative is to highlight all iTunes Media in WMP and choose "Delete from libary only"
That or, as suggested, do not use WMP at all.