After much back and forth trying to figure out what was causing my memory problems in Vegas upon rendering, I stumbled upon a solution which flat out works, so I wanted to pass it along.
Symptom is basically an error pops up stating that there's not enough memory available as I render a project. Doesn't matter to what type.
In a Sony KB article, it states to turn down the Dynamic RAM Preview amount to something like 64MB. That didn't work for me, so I set mine to zero. Voila, renders fine.