Well if your rescue disc cannot find the Linux install, something much worse than a video driver mishap must have happened.
If your rescue disc DOES work though, and you can get access to the installation's files and directories...
I never use pacakages, or I try to use them as little as possible for various reasons. I have had exactly the problem you had on Fedora Core, and I solved it (manually) like the following...
How I broke it:
First, I was booting in runlevel 3 (text mode) and not starting X windows automatically on boot (runlevel 5).
1. Downloaded a new NVidia Linux driver
2. Ran its install script, but for somer reason it complained that my card wasn't a Nvidia card (the card took a zap from a failing power supply, which somehow "partly" broke it)
3. After this, typing "startx" just resulted in a blank screen, just like yours now does on boot.
How I fixed it:
1. Downloaded an older NVidia Linux driver I knew worked with my older, damaged card.
2. Tried to install it, but the install script complained that it could not find my kernel headers.
3. Ok, got the kernel source code.
4. Install script still complained that it could not find the headers.
5. Ok, compile the kernel source code for my running kernel.
6. Ran the script, and voila! It worked.
7. Did startx, and there it went...
I. e. in your situation you probably need to some kind of package rollback. But, typically, since you used packages, you don't know exactly what the upgrade / package install broke. I do suspect though, if you manually do what I did above (edit /etc/inittab to boot in text mode, install the driver package for your card, edit /etc/inittab to boot in GUI mode again) you might get your system going again.
However, the fact that your rescue disc doesn't work probably obviates the above and (horror of horrors on a Linux system) you might need to completely reinstall Linux - and stay away from these types of package updates in future.
If you have to do something that is critical to your system, do it manually - even if it is tougher or more complicated than just dropping in a a package. You won't regret it. (Like you're now regretting the update / packaged driver install that broke your system).