Anybody know about iTunes??

did soem digging for u.
came across this page : http://www.osxhax.com/archives/000046.html

"Thanks to the MPEG4IP folks... Go fetch the MacOS X MPEG4 tools here. Using them you can delve into the secrets of the files iTunes makes.

Having done this, I've figured out that m4a and m4p files are really mp4 files. In fact, if you rename an m4a as an mp4, Windows QuickTime will play it perfectly, and as a bonus will extract a WAV file if you like.

Using mp4info, you can peer inside an MPEG4 file. On an m4a file, you see the excpected: a single AAC encoded audio track. On an m4p, however, you see an "unknown" encoding audio track.

These are command line tools, so you will need to play with the terminal to use 'em, but they seem darned useful.

In the meantime, if your goal is just to be able to share your m4a files (encoded from CDs or what not) with Windows machines, just rename them mp4 and play them from Windows Quicktime 6.1 (or, of course, extract the AIFF from them on the mac)."

after further reading it mentions you can bring over your M4A files as MP4 but not M4Ps.

aparently If you install the 3ivx codec for Windows, Windows Media Player can play .m4a files perfectly. However, it doesn't support iTunes' file tagging.

there are progs for the Mac that can convert the files to mp3 or whatever you want but i cant find one for Windows :/

just found this page: http://www.pmbrowser.info/hublog/archives/000316.html

links to: http://www.pmbrowser.info/hublog/faad_plugins.zip

which is "an input plugin for WinAMP that plays AAC files (.m4a) encoded by iTunes.

It plays the previews from the iTunes Music Store as well, if you change the filename suffix from .m4p to .m4a or .mp4"