Want to add my two cents about Dynamic Ram Preview.
My computer will start to render fast then slow way down to a crawl and
I would get horrible bottle necking issues.
So I set the Dynamic Ram Preview to 0mb just before I rendered and whoa.
The computer will keep all the processors (4) at a constant rate the whole render time. Pretty good speed as well.
Vegas 10e 32bit AMD Quad 4gb Ram Windows 64bit 7 Home premium. Rendering 1920x1080i to MPEG2.
Of course I have Dynamic Ram at 1024mb when editing.
Give it a try.
josh