I want to enable gd library support for php but I don't know how to do that. Please help me, I have a Fedora2 machine with CPanel.
Thanks in advance!

do a
./configure --help

and see the entry on gd.... should be something like

./configure --enable-gd-blah-blah

then you:
make && make install

ur php should have gd support now

Yeah you can do it silhouette's way or use cPanel's apache recompile located at /scripts/easyapache and pick what all you need installed.