Installing extensions (GD) - trouble

I am running RH 7.0 and installed PHP with the RPM and recently upgraded with the latest RPM of PHP. I need GD support now. Is there anyway I can just compile GD extension instead of the whole thing? Or can I compile the whole PHP and just copy the gd.so over to my running PHP dir? Also, I am already trying to compile the whole thing, but I can only get it to work when I config with --with-gd=[build dir] and nothing like /usr/lib where it actaully is, would there be any furture problem related to this? And is there anyway to fix this? Jason Lam