Is your monitor actually capable of 1024x768@76mHZ? Do your monitor settings in the XFree86 configuration file reflect that?
The drivers don't control what resolutions are displayed; the monitor does, and if it is not set correctly, XFree86 will not display at resolutions that the monitor can actually do, because it simply doesn't know that it can.
Other than the fact that you're not getting the resolution you want, are there any other display problems? What resolution are you in fact getting? What make and model of monitor are you using? Do you have the manual available? Did you set custom horizontal and vertical refresh rates using the information in the manual, or did you use default settings (either for your particular monitor or really "default" settings)?
Even if you are using the settings for your actual monitor model, you may still need to enter custom refresh rates. I have a similar problem with my monitor (an Eizo FlexScan F550i-W). This monitor often appears in the list, but those settings will only allow the monitor to use the highest "recommended" resolution (1024x768), even though the monitor is in fact capable of displaying at 1280x1024 (which is my preferred resolution). This occurs under both Windows and Linux, as apparently Eizo, "for my own good", just leaves out 1280x1024 as a supported resolution, in its official monitor specs/drivers.
Once I actually set the horizontal and vertical refresh rates to the ranges listed on the Eizo website for this monitor, 1280x1024 becomes available to me (under Linux; under Windows I have to say it's a different monitor, as I can't set my own refresh rates under that OS

).
And of course, in all your driver changing, the monitor settings are probably the one major element you
didn't change, so it's not surprising that you didn't get different results.