Maybe I'm missing something, but I don't see how .NET could need 512 megs of RAM. The worst-case I can think of is if you move to IA64 (doubling memory usage because of the doubling of pointer size), and then the garbage collector is tuned shamefully badly (again doubling memory usage). Together that would take a system needing 128 MB to 512 MB.
But I don't think that IA32 is going to die for a few more years yet, and I'd expect a great deal of interest in tuning gc performance since memory locality is so critical to decent software performance.
What am I missing?