ACPI is not necessarily the reason for your system crashing.
ACPI, or Advanced Configuration Power Interface, is one method used by Win2K to control your system devices and resources.
Most people notice that in ACPI mode, Win2K puts everything on one IRQ. In ACPI mode that is how it assigns its plug and play resources. Most people have no problems, other people do have problems. Usually it's all assigned to IRQ9...supposedly it's used as a gateway to virtual IRQs above 15.
Anyway,
here is the article from Microsoft dealing with it.
If you want to manually assign IRQs, or just let Windows do it properly, you have to change the ACPI mode HAL to Standard PC HAL.
To do this, go into Device Manager, and look under Computer. It should say Advanced Configuration Power Interface PC. Change this to Standard PC by changing the driver. Then reboot. Hopefully it should come out OK. This does not work every time, and sometimes causes your system to go a bit loopy.
If you need to reinstall, hit F5 while it is detecting all the devices right at the very beginning to manually select the Standard PC HAL. You may also need to turn ACPI off in the BIOS if you have that option.