Hi, just been thumbing through some stuff on vista SP1 and mainly been focusing on the ram issues. Ive found out that if you have the 32bit version of vista (regardless if its basic or ultimate) the service pack will not change the OS so you will be able to use more than 4 GB. You will only be able to use 3.5GB.
However the service pack will effect 64bit versions of vista. Home basic will be able to with stand up to 8GB, premium 16GB and enterprise and ultimate will be able to use a staggering 128GB of ram.
Heres one of the links if you have a nosey.