I did a 'sudo yum install kmod-nvidia' for my brand new Dell machine and it installed it and all its dependencies. But now when starting up it freezes during the bootup sequence, at different parts. I'm afraid I'll have to reinstall the whole system.

Is there a way to undo the yum installation so that I can boot back into the system? I tried using the same Fedora 17beta installation DVD to use its recovery mode but that wasn't working too well in the first place.

Is there a way to do it with another Linux installation DVD, like the one for CentOS 6.2 which I think might at least get me into recovery mode. But what could I do from that point?

Boot into single user mode so that you are not using X.
Then use yum history to go back in the install list.
Man yum

The release version should be out in a couple of days.
( Today it says May 29 http://fedoraproject.org/wiki/Releases/17/Schedule )

fedora 17 is not officially to be released until the 29 th

so UNLESS you can fix and submit a bug fix
I would NOT RECOMMEND using a early PRERELEASE version of fedora
UNLESS YOU CAN FIX IT ALL ON YOUR OWN

then for about 3 weeks after there will be about 3 gig's of bug fixes to fedora 17
so it will be NO WARE near stable until early July