I've got a CD full of MP3 files (old radio comedy shows) which will play on my computer (and on an MP3 compatible CD player) but which my MP3 player won't recognise. Your problem seems to be rather similar (i.e. Windows Media Player sees the files as a 'non-standard' form of MP3).
For me, the solution has been to load the files into Audacity, and then to re-save them in MP3 format. My MP3 player then recognises the standard format used by Audacity. (It's likely that Windows Media Player will also recognise your files once they've been re-saved in this way).
If you've not already got Audacity you can download it here:
http://audacity.sourceforge.net/
(It's free and deserves a place on everyone's PC).
In order to be able to save files to MP3 format you'll also need the LAME MP3 encoder:
http://audacity.sourc...?s=install&i=lame-mp3
Chris