1. you shouldn't be running yur laptops vista disk on another computer as its against MS licensing rules and they may well in validate your license number.
2. graphics will be terrible until you load the graphics driver for the Dell
3. you wo'nt get sound until you load the sound drivers for the Dell
4. yes you can load XP back on if you still have the licence number on the sticker on the Dell then just borrow a XP CD. and use the nmber off the DEll.