Upgrading from version 6 mid project
 

I was thinking of upgrading to Version 9 or even 8 and am wondering how that will affect current unfinished projects in Version 6. Will the project in 6 automatically jump to version 8 or 9?

If you open and save it in V8 or V9, then it can't be opened again in V6 as Vegas is forwards compatible but not backwards.
What I do is save the existing version under a new name such as myproject-V6.veg.
Then, when I open it up in a newer version, save it as something like myproject-V8.veg or myproject-V9.veg.
This way, you're protected in case of unexpected problems.

Having said all of this, I make it a rule to NEVER change software versions in mid stream.
V8 should be OK but there are reports of several different bugs in V9 that would make me very hesitant to switch to this version until they get resolved with at least a 9.0a update.