installing xp over vista

I have an hp pavillion m9000t it cam with vista home I want to down grade top xp for my software i can use.I been hearing lots of ways but none seem to work.One person told me to go to bios and change sata to ide? how does that work if my pc doesnt have ide.I have 2 500 gb sata hard drives.Then people keep telling me to go into bios and disable the hard dives and that didnt woek either.Did they put something in my hp to where I cant put xp in I have all my drivers for xp or maybe should i install my xp drivers then put the xp disk in.I been tring for 2 months and noone gave me anything that works I hope someone knows about this and can tell me