x-org configuration - help!

ok, this has been really frustrating. it is proving incredibly difficult to get X(org) to run at a decent resolution on a machine I have set up.

i want to run my screen at 1152x864 at 75Hz, but it is only allowing a maximum of 55hz. The screen is physically capable to run at this resolution at 75hz, because I have tested it.

Firstly, I can't find any decent tools to change settings. I only eventually found "xrandr" to change resolution, but it only allows resolutions which are specified in "xorg.conf' (i think), and I don't have a clue where it is getting the refresh rates for those values. why do all of the X tools have such inane, unintuitive, non-descriptive names!

So how do I add a 75Hz mode?
I have heard of two options, but one of them has not yet worked for me, and I cannot figure the other out. Alternatives would be apprectiated.

1. Add "ModeLine"s to the "xorg.conf" file. (could not figure this out)
This is really poorly documented. I don't know how to get the required information either (all of the sync rates.
They look something like this, though this obviously is the wrong refresh rate.
# 1152x864 @ 85Hz
# Modeline "1152x864@85" 119.651 1152 1224 1352 1552 864 865 868 907 +hsync +vsync

2. Running "dpkg-reconfigure xserver-xorg"
I have tried this a number of times, but it has not worked. When I removed the default resolution (which was too large, and only runs at 60hz) and then added the desired resolution (1152x864@75Hz). However when I restarted X, it starts in 1024x768, without the option to use 1152x864.

Any ideas how to set the resolution?