It's worth clarifying the point on whether "your software needs to be built for PAE" and from previous comments on last weeks show:
Firstly, let's be clear: AWE is not PAE. The first is about having more than 4GB of data in a process. The second is about having more than 4GB of RAM in a computer. (http://blogs.msdn.com/b/oldnewthing/archive/2004/08/19/217087.aspx). You can use AWE without PAE, and you can use PAE without using AWE.
Secondly, unlike AWE, PAE affects only things that look at physical addreses, i.e. some kernel mode drivers and the memory-management in the kernel itself - it doesn't affect normal user-mode programs. Consequently, to use physical memory above 4GB on a 32-bit system, only your kernel and some of your drivers need to be PAE aware - i.e. the ones that allocate physical addresses but foolishly assume that the physical addresses are 32-bit (physical addresses are actually 56 bit, just to be confusing). This truncation is the reason why 32-bit Windows chooses by default to ignore physical memory above 4GB and why it is disabled for Client SKUs.
You also need to be running the PAE version of Windows Server. There's a flag in boot.ini (or bcdedit) called /PAE, but this has been enabled by default ever since XP SP2. On a side-note, PAE is a requirement of hardware-DEP, so if you have DEP enabled, PAE is enabled. It's also a requirement of Windows7, so if you're running Windows7, you've got PAE.
Here's a good summary for the insanely few of you that actually care: http://superuser.com/questions/367490/can-a-32-bit-os-machine-use-up-all-8gb-ram-20gb-page-file
Anyway, all that said, unless you've got a really good reason not to, you should be moving to a 64-bit OS. That way all of these complicated things just work and you don't have to think too hard about it.