Sound driver XP vs Win7

Hello,

when, i was installed windows xp on my laptop(brand- lenovo, model- g550)... it cant play sound ..and said that no sound driver was installed or there is the problem with your sound device and windows media player alsi said that it cant play file..but when i installed windows7 on my laptop thn my sound works...nd i can play the songs..now but what is the problem with windowsxp..even i got theccd from lenovo..but the sound driver they give me ..its not working,...
plzzz help me...../////??????????