You do not indicate what version of ubuntu you are using...
I use a 64-bit version of Mepis and i use the LiveCD to make these changes with the Mepis assistants, it is different in Ubuntu... I have also use the liveCD as a super user to edit grub, find it quite easy...
Hope this helps...
Change Boot Options Permanently On An Existing Installation
These instructions only apply to systems that use Grub - Ubuntu's default boot loader.
For Ubuntu 9.10 (Karmic Koala), please see Grub2
https://help.ubuntu.com/community/Grub2
In order to permanently change your boot options, you'll need to edit the /boot/grub/menu.lst file.
Before you begin, open a terminal window and type this command to back up the file with a copy that has the current date and time appended to its name:
sudo cp /boot/grub/menu.lst /boot/grub/menu.lst.`date +~%b-%d-%Y~%T`
If the system or /boot partition has changed and the user suspects the partition is not correctly identified by Grub, run this command to obtain a list of partition UUIDs. Note the system or /boot UUID and compare it to the entry on the kernel's UUID line once the kernel menu is opened:
sudo blkid
Type this command to edit the menu.lst file:
sudo nano /boot/grub/menu.lst
(You can edit this file with any text editor, doesn't have to be nano) Use your arrow keys to move your cursor to the line that starts with "# kopt=".
Add or subtract whichever boot option(s) you'd like to add to the end of the boot command, with a space between each one.
Save the file.
For nano:
Press the Ctrl and o (this is the letter o) keys at the same time. Verify that the filename is correct (edit the filename if it's not) and press the ENTER key to save the file.
Press the Ctrl and x keys at the same time to exit the editor.
Type this command to update the menu entries in the system:
sudo update-grub
The command may present a message indicating that a new configuration file available: "Do you want to keep the existing one for menu.lst". Select Use Package Version. If you select to keep the user modified version, your changes to kopt won't be applied to existing boot options.
Note: If you edit the menu entries directly from Grub and not with a text editor your changes will disappear the next time update-grub is run, for instance or when the kernel or grub packages are updated.
Common Boot Options
This list is not comprehensive but it contains some common boot options. When presented with the text on the screen "boot:" then the boot options below can be given. They must have the kernel name before the option.
Example
Adding the vga=771 option:
boot: /boot/vmlinuz-2.6.15-26-k7 root=/dev/hda1 ro quiet splash
boot: /boot/vmlinuz-2.6.15-26-k7 root=/dev/hda1 ro quiet splash vga=771
Options can be used together such as in this example:
/boot/vmlinuz-2.6.15-26-k7 root=/dev/hda1 ro quiet splash noapic nolapic
Alao note: hda1 could be sda1 on your hardware...
APIC Kernel Options
acpi=off OR noacpi
This parameter disables the whole ACPI system. This may prove very useful, for example, if your computer does not support ACPI or if you think the ACPI implementation might cause some problems (for instance random reboots or system lockups).
JR