In the past I always left the previous version of Vegas, etc. on the machine while I tried out the new version. This time, in preparation for installing 8.0, I uninstalled previous versions of several Sony products, including Vegas 6.0, Sound Forge 8.0 (9.0 works well now), etc.
Now, Vegas 7.0d (never went to e), which I expected to keep on the machine while starting to use 8.0, is unstable. It crashes and will not render (won't start with AVI and won't go for more than a minute with mpeg2). I can only assume that previous versions pulled out drivers, files, etc. that 7.0 was using. I always thought they were totally independant--guess not.
This is just a warning to those that may attempt something similar.
Now I will uninstall 7.0, re-install 7.0 with the latest d update and see if it is stable--before I go messsing around with 8.0.