That RPM is at (i'm assuming i386 here): 
http://download.fedora.redhat.com/pub/fedora/linux/core/updates/6/i386/libstdc++-4.1.2-13.fc6.i386.rpm

so do:

curl <that URL> | rpm2cpio - > /tmp/libstdc++-4.1.2-13.fc6.i386.cpio
cd /
cpio -iv < /tmp/libstdc++-4.1.2-13.fc6.i386.cpio
rpm -ivh <that URL>

that will short-circuit the RPM's files on to the filesystem, and then follow 
that up with installing the RPM on top (you may need --force options).

After that's done, you can try doing a yum upgrade (it's pretty easy) if you 
have the bandwidth.  You will end up with an updated F7 system at the end.

http://fedoraproject.org/wiki/YumUpgradeFaq

-Dave

On Saturday 01 September 2007 09:58:37 am Jim Scott wrote:
> I recently upgraded to Fedora 7. I was cleaning up some stale Fedora Core 7
> packages. I made the mistake of removing libstdc++-4.1.2-13.fc6 because I
> was planning to install libstdc++-4.1.2-12.fc7. Of course, now I can't run
> yum or rpm to install the new package because both applications depend on
> libstdc++.so.6, which is no longer installed.
>
> Are there any options to correct this? I'm trying to build gcc from source
> now, which I think would fix the problem. I can't reinstall Fedora 7 from
> the DVD (the DVD passes the media check, but the DVD hangs at the start of
> the install process). Thanks for any suggestions.