i know this doesn't exactly 'fix' your problem. however, when you say you're rendering the files, do you mean just rendering for a preview or rendering as in exporting to a file (DV .AVI, MPEG-2, etc.)?

if you're looking for a less-intensive way to process video to encode to MPEG-2 from within Vegas, you may want to check out DebugMode's FrameServer application. using it cut my encoding time by 50-70% (was using CCE's plugin for Premiere, to now using Premiere > FrameServer > CCE).