First of all you have to get it
I suppose you already have it in RPM or tar.gz format. The thing you have to do first is uninstall the new gcc version and then install the old gcc.
Uninstalling is done with:
rpm -e gcc
I think this should do it or produce some errors. If it produces an error that the package couldn't be found, try appending the gcc version.
Or check the fedora CDs for the gcc RPM and use the name up to .i386.RPM
Once you have it uninstalled, you have to install the old one.
You do that by rpm -i gcc.xxx.rpm
or from the source files:
tar -zxvf gcc.xxx.tar.gz
tar -vjxf gcc.xxx.tar.bz2
This should install the old gcc
Good luck! Peace!