GlobalMemoryStatus is the one I was looking for. According to the online documentation, GlobalMemoryStatusEx is only supported on Windows 2000.
I have written a small module available over at Win32::MemoryInfo. It almost cries out to have something else added to it before I submit it, though. I noticed a function called GetSystemInfo which will return processor information that might be a nice inclusion.

Guildenstern
Negaterd character class uber alles!