This is correct. XP Pro/Home x86 32 bit will only address 3 gig of RAM by default, 1 gig virtual. This is a "4 gig" process limit.
I'm unsure what you're planning on getting out of 2 gig -> 4 gig. In this memory model and for valid usages > 2 gig, you're usually looking at 64bit cpu/64 bit memory addressing.
Never fear though as the boot.ini can be modified to create a virtual/per process improvement in >3 gig XP environments using good old 32-bit XP Pro or Home through Physical Address Extensions (google AWE for more info on this as it allows a 3gig per application memory space, 1 gig for kernel address).
To do this, once you have 4 gig installed, manually edit the BOOT.INI file on your boot device and add /3GB option.