U need to install vista after XP.Than only U will be able to use both OS.If U install XP after vista,than I am scared U boot file will get currpted and U wont be able to use vista.
And If U are facing problem with XP and vista boot,than read here.It may help u.
Vista Boot solution
For vista Driver,U need to down;oad it from ur motherboard manufacture's website.No other resource.