Win32 only "sees" around 3.3 GB of RAM, but on some machines - like my Mac Pro - it even only sees 2 GB RAM. This depends on the chipset of the computer and what-else-not.
Furthermore, there is a limit to the virtual memory that a 32-Bit application can use - which is 2 GB per application.
You shouldn't stick with 2 GB and, in my opinion, you also should no longer use a 32-Bit version of Windows unless you have a very compelling reason to do so (like an application that is incompatible with Vista 64).
You should get yourself a copy of Vista and install the 64-Bit version on your notebook. In case your notebook does not come with a 64-Bit compatible version of Boot Camp, download the 64-Bit driver disc for the Mac Pro from a Torrent. (I've done this for my officially unsupported Mac Pro and it works great!)
Most of the drivers come with Vista already anyway. You'll need the Boot Camp drivers for the "fancy" Apple stuff like the backlit keyboard, the iSight camera and Apple's proprietary BlueTooth chip. Almost everything else works out of the (Vista-)box or with drivers from nVidia or ATI.