What resolution are you trying to get? If it's one that's not supported in the Xorg i810 driver for the i945 chipset (e.g. 1280x800), then you've got to run the i915resolution binary to patch the video BIOS in RAM.
I'm using the i945 chipset in a Dell Inspiron 6400 laptop with a 1280x800 wide screen, and none of the more than a dozen Linux distros I've tried (except for SLED 10) supports this resolution. I always have to do one, two or all three of the following:
1. run # ./915resolution 3c 1280 800
2. add a Modes entry for 1280x800 in the Screen section
3. add a Modeline in the Monitor section
I also often have trouble with the i810 driver that goes away when I use the vesa driver (i.e. in the Device section replace "i810" with "vesa").