This I might have to step up to Vista ... ulp.
[EDIT:30/02/2009] Prompted by an anonymous comment on this post, I felt it wise to expand on my endevours, or at least provide some more information. Anon is indeed correct that 32 bit OS's are limited (as far as Windows goes) in accessing RAM...
- Here is Microsoft's memory access page: http://msdn.microsoft.com/en-us/library/aa366778.aspx
- Crucial's memory scanner: http://www.crucial.com/uk/systemscanner/index.aspx