well you need to convert all your iTunes music to MP3, and don't worry this is really easy.
open iTunes
Right click the grayish area where it says 'Name,' 'Time,' Album,' etc
with the menu that opens, select 'kind'
now sort your music by kind (1 click the 'kind' heading)
select all the songs that are 'AAC audio file'
Right click the selected songs
select 'create MP3 version.
once itunes creates MP3 versions open Windows Media Player
click the arrow below 'library'
select 'Add to Library'
click 'OK'
all your songs that were converted to MP3 should appear once the search is finished
Hope this helps

PS your original songs are uneffected.