I ve done a Belgium music Mod just with Belgium music from belgian composers and Belgium military marches.
So when you play Belgium you can hear between the normal music the belgium one.
Doanlowd these mp3 here :
http://www.mediafire.com/?wsjzgirj3p9e9lh
then unzip the files (with winrar) in your sounds folder:
Pride of Nations-> VGN -> Sounds
Then open the musics.ini with notepad (this file is in the Sounds folder)
and add copy paste these line at the end:
Music143 = BEL_ALL_La_BRABANCONNE.mp3
Music144 = BEL_ALL_Scene_de_Ballet_De_Beriot.mp3
Music145 = BEL_ALL_Mars_vh_1ste_Reg_ Gidsen.mp3
Music146 = BEL_ALL_Mars_van_het_2de_REGIMENT_JAGERS_Te_PAARD.mp3
Music147 = BEL_ALL_OPHELIE_LEKEU.mp3
Music148 = BEL_ALL_Marche_du_12e_REGIMENT.mp3
Music149 = BEL_ALL _Mars_van_het_1ste_REGIMENT_LANSIERS.mp3
Music150 = BEL_ALL_Cesar_Franck_Symphony_D.mp3
Music151 = BEL ALL_Marche_ du_1er REGIMENT_de_GRENADIERS.mp3
Music152 = BEL_ALL_Marche_de_l_ECOLE_ROYALE_MILITAIRE.mp3
Save the file and that it. if you have allready add other music change the nummer to continue the sequence.
enjoy