What format and container are you currently using, and rendering as?
I made a couple of gaming vids, and for the second I used Vegas for the first time, it'd take friggin' ages to edit due to the large FRAPS filesizes. I tried various formats and containers to get the best image quality/filesize ratio, to both edit and upload to YouTube.
I found rendering in full resolution, was best using Sony AVC (mp4), I rendered at 50FPS with a high bitrate.
For me, this was the best solution, as I was able to keep the resolution, and only lose a very
minor amount of quality. Also, 6GB files became 600MB or so, so the strain on my system when editing was down a massive amount, as was playing the file, aswell as storage space saved.
For you, it depends on what exactly you're rendering, and if MP4 is good enough quality for you.
Render a small part of it (the little yellow bar above the movie timeline, just drag that to a smaller size. Sorry if you know this already, just throwing it in there), and see how it fairs for you.