Mental Ray Renderer freezes 3DSMax 9 64-bit.

After the Final Gather pass, mental ray will freeze up my installation of
3DSMax9 64bit.  The rendering job DOES complete, but the buckets stop moving and
then all of a sudden the final rendered image appears--all this happens at the
expense of no other program being responsive.  Has anybody had this problem?  

I'm running:

Intel Xeon Quad-Core 2.3Ghz
4GB RAM
NVidia QuadroFX 4600
WindowsXP 64bit edition
Max 9 64-bit

I tried to disable the multi threading option in the Rendering tab in
"Preferences" dialog, but that did not help.  I figured Max is taking
advantage of all the "cores" of my processor via multithreading , but
I suppose it's not.  

Has anybody encountered ths problem?

Is there a way to limit the amount of RAM that Max9 64bit can take up?