I really have had nothing but problems using Vegas 8 in comparison to Vegas 7....

I made an entire short film (22min) with 5.1 audio and many, many tracks but in Vegas 8 it stutters and just plain runs terrible on a much faster computer.

When I made my movie, I had a Pentium 4 EE 3.4.... I know have SATA and a Duo Core 2 @ 3.2 and it runs simply terrible. The only thing it does that I can't get 7 to do is edit xvid files properly. It claims it doesn't have the codec even though I know it's installed on my computer.

Vegas 8 however edits xvids fine but when the layers start to pile up, cough 2-3 layers tall.......big time lag for no reason. No FX or anything, and.....it's running in preview mode....omg.....

I had to use BEST mode to get lag using Vegas 7.

Anyone know of any fixes for this Vegas 8 deal? I'm using 8.0b. I'm not gonna upgrade until I decide whether or not I'm going to try to go back to 7 or not.

It could also be partially that you're editing XVid in Vegas 8 unlike in Vegas 7. XVid is highly compressed so I'm not surprised it would take longer to decompress each image (i.e. cause stutter) than when editing something like DV. Anyway, there's lots of variables that could be contributing to what you're seeing.

It's Xvid responsible for your problem.
Although Vegas can decode it, it's not native (no NLE natively ever will decode Xvid, it's a delivery format) and therefore requires system calls to access a decode. TIF images and Quicktime frames are similar. Vegas requires Quicktime to be installed in order to decode those, and Vegas uses Quicktime to "translate" those files. As a result, the editing experience of these file formats is very klonky and slow. That's not Vegas' fault. Give it a codec designed for editing, and it hums along nicely.