also remember that the memory limit in a 32bit operating system includes your graphics card, so it you get one with 500MB or 1GB thats going to wipe a considerable chunk of the amount of memory you can use for your system.
I'm my eyes its the only way to go these days. the only driver problem i have had with vista or XP 64bit is my plotter at work doesn't have a 64bit driver so i cant print in magenta, yellow or blue (but why would i want to do that anyway??) blacks fine for what i do.