Using 32-bit key on 64-bit Windows

So, I have a notebook with a Windows operating system pre-installed. The thing is the version installed is a Windows Vista Professional 32-bit. The CPU is a Core 2 Duo. The default memory is a mere 1GB but with an additional slot for expansion purposes. Now, I think why I'm saddled with 1GB. Why can't I upgrade the memory all the way to 4GB?

But wait, didn't they say you couldn't take advantage of the 4GB memory if your OS isn't a 64-bit? That's still true but if you don't mind the extra work, why not reformat your unit with a 64-bit version of Windows Vista?