In the Red Hat menu, there's probably some graphical utility to change it. I'm not sure. You should learn the standard way though.
As root, open up /etc/X11/xorg.conf with your preferred editor. Scroll down to Section "Screen". You should see a list of resolutions there. Those are the resolutions X will try by default. You should add the one you want to each of the entries labelled Modes. Then restart X and see if it works.
As far as cleartype goes... Are your fonts not already antialiased? Please give more details as to what you're talking about.