This is something I hadn't appreciated earlier. 32 bit Windows can support more than 4Gb of RAM. The link is a very well written article and worth some time if you have interest.
The main point to think about when trying to get your head around this is that a modern OS doesn't allow applications to access memory directly, but via virtual memory pages. These pages are mapped to physical memory in a way the OS decides given the ability of the hardware. 16 bit Windows was able to access more than 64K memory, and in the same way, 32 bit windows can access more than 4Gb memory. 32 bit Windows drivers need to deal with 64 bit numbers to do this, but this has been part of Windows since at least Windows 2000 and probably Windows NT. Note, of course, that any individual 32 bit app can only access less than 4Gb RAM, we're talking about the OS here.
The reason Vista 32 and others only report less than 4Gb RAM is a licencing one! See the article.
Obviously it is in Microsoft's interest to have us all using 64 bit Windows asap. That's fine with me.