Running VIsta 64 on a Q6600 4 gig ram .. I'm working in SD with standard AVI DV files and some Mp4 - and PNG and JPG stills. Had some problems with media on V9. It would be fine for awhile, then simple things like cross-fades would not preview without video breaking up. Cure was to close Vegas 9 and reopen it. -- On occasion, "undo" would freeze V9. I kept working in V9 as I like so many of the features -- So often in the past the issue was always MEDIA and the right CODEC. So I kept looking for the next K-Lite update.... ---- Just installed the new K-Lite codec for 64 bit and WHAM! .. No more problems. Vegas 9 running smooth as 8.0c ever did for me. Just finished a 10 min piece without a hitch. Here's a link to the new CODEC which is working very nicely for me. I can't say it will cure anyone elses problems but worth a shot. It's free. It's version 2.4.5.

K-Lite 64 bit codec