Reinstalled xp after Vista . USB port not working

Question

I had xp sp2 on my system for a few months.
i decided to install vista ultimate on my system.
the vista installation woked fine in all respects.but still i want to go back to my xp sp2
the problem is that when i installed xp sp2 the usb ports are not working
(they are providing power i.e the light on the usb mouse is comingbut the mouse is not ing detected) even the pendrive is not working

there is no hardware problem i checked it out by reinstalling vista
the usb ports are working fine

i have tried 2-3 different installation cd's

any help

also the drivers for the laptop fail to install. specially the chipset which i am desperately trying to install....