Here is some information from
http://grumpymole.blogspot.com/2007/...arameters.html
1. Changing Boot Parameters Temporarily
Generally, this is used when you want to try a parameter change to see it is beneficial to your system. When the PC boots up, you will see the Grub countdown, which is set to 3 seconds by default. Press "Esc" to intercept this countdown and go enter a Grub menu. Then
Press 'e' to start editing.
Scroll down to the "kernel..." line (Normaly only one line down). The is the line that tells Grub which kernel to boot with and the parameters to be passed to the kernel when it boots are placed at the end of this line.
Press 'e' again to edit this line.
Move to the end of the line. You will see any existing parameters and can add other new parameters to the end.
Parameters are separated by spaces and are mostly either a single word (e.g. nolapic), or an equation (e.g. acpi=off).
All you have to do is enter the number "1" or the word "Single" without the quotes.
Once you have added the parameter to the end of the line, press Enter to accept the editing.
Then press 'b' to boot using that kernel and those parameters.
Remember, this change is not permanent. At next boot, it will be undone.
Now go back and modify your xorg.conf file.
Good luck