Even though PAE is enabled there still are license restrictions on the maximum ram windows can use. If you need 32 bit and more than 3GB of ram (the limit is really 4 but a good chunk is taken up by your IO) you will need to go to something like Windows Server 2008 Datacenter or Enterprise edition.
There are patches that can remove the license restriction (that link is for Win 7 not Vista), however it is much more reliable and safer to just run the 64 bit version of windows.