wow this is nice timing, today i was just planning to upgrade my RAM aswell, having only 2gb in my laptop. i was only gonna get another 2gb Ram stick which would obviously give me 3gb total, and i was going to do this because having 32bit Vista, i probably wouldn't get the most out of 4gb..
but now i think I'll go for the 4gb and then dual boot my current x86 Vista with either Windows 7 x64 or Vista x64.
the only reason i wouldn't reinstall either of the x64 versions over my current x86 vista is because i just prefer keeping my legit version aswell. and i really can't be bothered having to deal with all those windows genuine cracks for a base OS.