As of June of 2007 one article outlines some advice for the average user about memory and which version of Windows to go with.
Overall
As things stand at the moment (June 2007), the sensible course of action for the vast majority of Windows users buying a new PC is to get a standard 32-bit WinXP system with at most 3Gb of memory. It'll come as close to Just Working as Windows ever does, and you'll be able to use as close to all of the installed RAM as makes no difference, if you don't go totally crazy with your video card choice.
If you insist on buying Vista version 1.0, it's
still not a bad idea to stick with 3Gb of RAM and use the 32-bit installation option, because 64-bit Vista needs 64-bit drivers. 64-bit drivers are not necessarily fully cooked, or even available, for the hardware you want to use. Many 32-bit XP drivers work in 32-bit Vista (subject to the limitations I explained back in the
first Ask Dan), but
no 32-bit XP drivers work in 64-bit Vista.
(If you've got 4Gb of RAM, by the way, the Vista installer
may not work anyway. You can work around that problem, if you have it, by pulling some of the RAM while you install Vista, then putting it back.
Apparently Microsoft limit the maximum available memory in 32-bit Vista to 3.12Gb anyway, though, so it's hardly worth the trouble of buying more.)
It won't be long before 64-bit Vista becomes a sensible proposition for people who want a PC with 4Gb or more RAM. Right now, though, there's very little point to it for normal users.
Yes, if you install 8Gb of RAM (the artificially-limited maximum for Vista Home Basic; Home Premium can take 16Gb) in 64-bit Vista, you'll be able to use more than 7Gb of that RAM, no matter what. But unless you're using 64-bit workstation/server applications (not just
Photoshop), or multitasking a whole
lot of big 32-bit apps, or running multiple
virtual computers on your one physical one, then the extra memory will only give you a small performance gain.
Small enough that if someone steals half of your memory, you may well not notice.
http://www.dansdata.com/askdan00015.htm
16gb of memory on a system running a 64bit OS sees only 7gb? Regardless I'll still be seeing the 32bit versions of XP Home and Vista Home Premium on the new build here with 2gb of performance memory rather then throwing money at nothing.