To remove ACPI try the following:
1) Run REGEDIT (Start --> run --> regedit). Go to the key
HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT\WINDOWS\CURRENTVERSION\DETECT
2) With the Detect key highlighted in the left pane, look in the right side pane for a subkey called ACPIOption. If it is there then double click on it and change its value to 2, then click OK. If it is not there then right click in the right side pane and select NEW, then DWORD value. Type in the Give the new key name of ACPIOption (mind the capitalizatin), hit enter. Now double click on the ACPIOption subkey and give it a value of 2, then click OK.
3) Reboot
4) Once windows is up again go in to Add/Remove Hardware in Control Panel. Tell it to detect new hardware. Accept the hardware it found and let it install the drivers. When it asks to reboot do so.
Have your Windows install cd handy. When the system comes back up it will start (re)installing a lot of hardware (drivers) and it will need access to the cabs on the cd. After its finished finding and installing the newly found hardware it will likely want to reboot again. Let it. If it doen't ask then do a reboot yourself.
At this point the ACPI bios based drivers should have been replaced with basic Plug and Play ones. You can check under device manager (System devices) to see.
Now the above method is not the most "tidy" as it will leave behind a number of no-longer used entries in the registry. Using the method of deleteing the Enum registry key first that was described in the article Nick Grana referenced will not leave behind these "old" entries. But the downside is that you may also have to reinstall drivers for various other devices you have (have added) sound cards, net cards, etc, etc). Your choice as to what ya want to do. It actually may be less painfull to just not worry about the left-behind entries.