Could not select visual on RedHat 7.3 (Linux)

I am a software developer on Linux. I am
developign aplication on Red Gat 7.3 and I
have installed OpenGl (from RedHat CD’s). When I am using the call glXChooseVisual
it returning NULL. So I could not proceed
further. I am having ATI graphics card
with 8 MB Video RAM and my scrren resoultion
is 1280X1024. What could be the problem.

B. Prabakaran