Can somebody help me downgrade my HP Pavilion dv8125nr Notebook PC from windows 7 TO VISTA PLEASE.?

Well, i had some quack repair my pc and he took my 80gb hdd and gave me 40gb hdd and the worst part is he moved back to india! and now he took me off xp and put me on windows 7 and boy i'm telling you my pc only lasts 20mins off the charger and on xp it would last me about 5-7 hours the thing i mighty slow and it takes forever to start up a program but now i heard of vista being able to be support my pc i called hp and they stated that 7 is not supported on my pc and it could possibly damage my pc so can someone help me downgrade my pc to vista or xp please.