I agree with Adam, if you get to a shell, there are ways to restore your...
I agree with Adam, if you get to a shell, there are ways to restore your system because you did an upgrade, not a complete reinstall (yet).
On the other hand, I would take Lew's suggestion and grab one of the lighter and newer distributions from the web and make sure you computer is set to boot to a CD. Using a Live distribution allows you to test drive the system to make sure it will run ok on your hardware before actually installing that.
If you are able to boot to a live CD, it is possible to see what software was installed on the broken system and reinstall that on a clean build but you would have to get into the live CD environment first.