I’ve been on holidays the last few days so I hope I’m not too late on this.
Upgrading to Vegas 8 Pro won’t affect any files currently on your system.
I do have to add one caution though and that is, if you do upgrade, to immediately save any critical project(s) under a new filename after opening them in the newer version..
For example, if the Vegas 7 file is MyMovie.veg, save the new one as MyMovie-V8.veg.
You may also want to consider creating a new folder (call it Vegas 8 Vegs), copy the Vegas 7 vegs to it, open and re-save them under the new name.