I don't have an R3240us, but I do have a compaq laptop and I found this site to be pretty helpful: http://tuxmobil.org/compaq.html
They have an R3240 listed, I don't know how different that would be from the R3240us. I had a look and the say its a widescreen one, and there's a section of the xorg.conf showing the refresh rates.
I used to have an xorg.conf using modelines on slackware 10.0, so I guess you should have no problems doing that. You could try using the refresh rates above when you do xorgconfig, then edit xorg.conf and put in the modelines that you used before.
Its always fun getting linux going nicely on a laptop