I am sorry to ask the question which doesnot belongs to this topic. I am using 4GB of RAM to all the XP32 bit machines.. In all the machines, when I check, how much RAM is present, XP shows only of 3.24GB in place of 4GB. So, I dont think that XP can support 4GB of RAM.
As far as I know it supports upto 4Gb but some of the address space between 3Gb and 4Gb is used for hardware, essentially the Graphics adapter. Explained here: