110.9MHz is the pixel clock--basically the inverse of the time delay between one pixel and the next. You are correct about the vertical and horizontal refresh rates.
The way I set refresh rate is to add a fully calculated Modeline using Colas XFree Modeline Generator
. Entering the values 1024x768, and vertical refresh of 60hz, it gives:
ModeLine "1024x768" 68.25 1024 1072 1312 1408 768 770 782 808 #60Hz
You want to edit your /etc/X11/xorg.conf file, inserting this modeline inside the "Monitor" section. Don't be surprised if there aren't any Modeline lines in there already--if none exist then xorg will use some standard resolution settings (which is fine if you don't care about having any control over them).
After editing this file (you need root access in order to make changes to this file), you can restart the X server display by pressing Ctrl-Alt-Backspace. This will rudely yank the GUI display out from underneath any programs you're running so quit any web browsers or other graphical applications before pressing this key combination.
When the X server restarts, one of two things will happen:
1. You'll be greeted with your familiar GUI login splash screen (possibly in a new resolution). Good!
2. You'll be greeted with a plain old text console display, possibly with some error messages with X complaining that it didn't understand something in the xorg.conf file. Bad.
In this case, you'll want to undo the changes you made to xorg.conf, and give it another go.
BTW, in order for 1024x768 to be used as default, you'll need to edit another part of your xorg.conf file--one which lists the available "Modes" to be used. You'll want to replace these lines with something like:
Modes "1024x768" "800x600" "640x480"
It's your choice as to whether you care about those other resolutions.