I don’t think sending the project will make a difference because you said that old projects that were fine on XP look bad too. That means your new project will probably look fine on our PC’s. If the text looks fine when previewed at full quality on the timeline it’s probably not the fonts either.
This points to the render as the only opportunity for a change. Try rendering to several different codecs across AVI, MPG, MOV and maybe even MP4. See if maybe some other software has caused a codec to be swapped. I know that I had horrible problems with having Nero Burning software on my PC. It inserted itself into my AVI stream and made all of my DV AVI renders from Vegas incompatible with Boris RED. I uninstalled Nero and everything worked again!
So what other video/DVD/multi-media software is on this new PC?
~jr
http://www.johnrofrano.com
http://www.vasst.com