I faced the same problem with RH7.0 detecting my 17' Datamini. But got no prob earlier with RH6.0,6.1 or other variants.
Belief me guys, even the lowest resolution won't work. What I do now is everytime after I startx I used Xconfigurator which will first detect my graphic card correctly and readjust my screen beautifully. But then it goes on to try to detect my monitor which will always fail and I have to quit with no option to save.
But The GUI will remain since my graphic card was detected and applied but after I log out and log in again...back t square one.
The moral of the story : When using Linux, find a variant that match your hardwares.
Good luck.