4GB of RAM works fine with a 32-bit operating system.
2 to the 32nd power = 4,294,967,296 (~4 GB), however, less is available to the
OS, since motherboard resources use some of this address space, and Windows
will only report 3.X (mine is 3,405,568 KB ~ 3.4 GB) available for Windows to
use.
Some have reported problems with certain mobos and 4GB RAM and 32-bit Vista.
I have no problems here -- Vista 32-bit flies and I seldom use over 45% of
available RAM.