We have a large Visual Studio 2005 C++/Mfc solution, 1 project with around 1300 source files (so about 650 .h and 650 .cpp files). We also use Boost and a few other librarie
If 1300 files are taking THAT long to compile then you are including waaaay too many header files that are unncecessary. I'd guess people have cut and pasted a bunch of headre files into a CPP file without thinking which headers they actually need so that loads of them are getting included when they ought not to be. I'm also guessing that you aren't forward declaring classes where you should be.
I'd suggest you need to spend some time going through your project and removing unnecessary #includes. I suspect this will fix your out of memory problems AND will improve your compile time.