changing resolution on laptop

[stm23]

hi, i'm having trouble changing the resolution for my dell inspiron 600m 
laptop (redhat 9) - i can only get 800x600. if i try & change it via "display 
settings" say to 1400x1050, i am told to log out for the changes to take 
effect.  i do this, but the resolution is still 800x600.  does any1 know how i 
can change this? - 800 x 600 is pretty limiting.....
cheers, sam