your boot camp partition uses NTFS, which OS X can only read. If you want to store all your music on the PC drive you will first have to get OS X to read and write to it
http://macntfs-3g.blogspot.com/
http://code.google.com/p/macfuse/
These two will allow you to do this (restart)
Next use the consolidate library command in iTunes to move (copy) all your items to a folder on the PC.
Select the command consolidate library from the Advanced Menu. This will copy all your itunes media to the PC folder and link the itunes library file to it
The files will now be on the PC drive while the library.xml file (the index as it were) will still be in the Users > Me > Music folder of your mac.
If you want this file on the external as well as well, copy it to external iTunes folder, start itunes with the alt key pressed and you will have the option to select the library file now on the external
Select the library file you just copied and now both your music and the library are on the PC
You can now delete the old Itunes folder off your mac
More info and what to do with itunes on the PC to acess the music are here
http://lifehacker.com/software/itun...sic-library-over-your-home-network-230605.php