You might not be aware but it’s possible to get a 32bit version of Windows 7 to use PAE (Physical Address Extension). That means that if you’ve got a 32 bit computer, you can use more than 4GB of RAM in it, or at least use all 4GB at the same time instead of having some of it restricted.
Server versions of Windows all have this capability, and Windows XP used to be able to do this as well until Microsoft patched the functionality out in Service Pack 1 since so many drivers had problems with it. Almost every driver today is made as a 64 bit application as well as a 32 bit one, so their architecture generally won’t have problems with PAE. In fact as of Service Pack 3, the only Windows XP driver that is known to not work PAE is the Microsoft USB driver.
That aside, here’s a patch by Unawave that will modify the Windows 7 32bit kernel to support 4GB+ of memory, it works on both service packs, but the included kernel is rather old and patching over it is probably a bad idea. There’s a more up to date version of the patch however that one has since been pulled since people complained that modifying your kernel was a “security flaw”. Unawave replaced it with instructions for performing the patch yourself.. I still think they were being a bit sarcastic there since the instructions involve signing your new Windows kernel before adding it to the boot-loader. If you follow them then you’re very confident.
Microsoft does limit the amount of memory their server systems can access as part of their licensing policy. However that shouldn’t apply to their desktop offerings since for them it’s supposed to be more a matter of stability and support. That being said if it does turn out to be a licensing issue, I’ll have to take the link down.