I thought I answered this (or an exact same) question on the Dell users forum. But, I would suggest 32 bit as Dell supports Vista 32 bit so you should be able to use those drivers
for Win 7 32 bit. If you go to 64 bit there are NO Dell device drivers and getting some devices to work may be a problem.
Keep in mind the install sequence (1) Install Windows (2) Install Intel Motherboard Chipset Drivers (3) Install device drivers including video, Dell sound drivers, ethernet, etc. HERE
is the Dell Vista 32 bit driver