Then why have I heard people say that 32 bit XP regognizes as much as 3.5 GB on some systems?
Reading up on it, it appears that Vista (in their uberest knowledge) decided to lower the limit in their operating system to 3.12GB in order to avoid conflicts. I believe what I said holds true for other 32bit platforms, though.
I'm getting the 4 gb of memory and then get a custom built one
64bit Vista will address in excess of the 4 (or in this case 3.12) gigabyte cap, but by definition a 32bit OS cannot handle more than 4GB of systemwide memory.