Server 2008 Standard, x86 (32-bit) is limited to 4 GB of physical memory, so there's no "configuration step" you can perform to get around that. Upgrading to the Enterprise Edition (of 32-bit Server 2008) will give you the ability to use up to 64 GB of physical RAM, with PAE enabled, of course, and there is a supported upgrade path between the standard and Enterprise editions of Server 2008, provided you don't change CPU architectures (32-bit to 32-bit or 64-bit to 64-bit). Pop in a Server 2008 install disk, choose the enterprise edition, input a valid serial and upgrade your existing Windows installation.
And, yes, it is still a supported platform that's commercially available...though it may take some searching to find.
Enabling PAE after installing the Enterprise edition, if it doesn't happen automatically, can be done with the below command from an elevated command prompt:
Bcdedit /set PAE forceenable
Following a reboot, PAE will be enabled, and you'll be able to make use of more than 4 GB or RAM. I don't honestly remember whether or not the upgrade process does this automatically, because it's been so long since I've actually installed a 32 bit OS.
Having said that, I find it difficult to justify having a 32 bit server OS around, let alone upgrading it. If at all possible, I'd just replace it with Server 2008 R2 or Server 2012 R2, and advise you look into doing the same... it's a fair bit of effort either way, and if I'm going to put in a bunch of effort, I figure I may as well just put it in once and get to a newer platform I won't have to worry about for many years to come.