How to set up an Advanced Configuration and Power Interface (ACPI) system running Microsoft Windows* 98 Beta 3
Windows 98 defaults to NO ACPI support, so you have to do this manually.

To set up Windows 98 as an ACPI system, run setup with the following command-line, case-sensitive switches: "setup /P J".

Alternatively, to enable ACPI after setup, simply go to the following key in the registry: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\Current Version\Detect.

Create a new string value called "ACPIOption" and set it equal to 1. Then run Add New Hardware (detection). ACPI should be detected and installed. After re-booting, all of your ACPI-enumerated devices will be set up again.

How to determine if Windows* 98, Beta 3, is setup correctly for ACPI when receiving an error message within Intel Power Management Analysis Tool (IPMAT) saying that target system is not ACPI-compliant.
Go into your device manager and look under the SYSTEM DEVICES section. Does it show any devices named "ACPI xxx"? (probably "ACPI Generic EIO Bus".) If not, then Windows 98 is not set up correctly. To set up Windows 98 as an ACPI system, run setup with the following command-line, case-sensitive switches: "setup /P J".

Alternatively, to enable ACPI after setup, simply go to the following key in the registry: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\Current Version\Detect.
Create a new string value called "ACPIOption" and set it equal to 1. Then run Add New Hardware (detection). ACPI should be detected and installed.

After re-booting, all of your ACPI-enumerated devices will be set up again. You should then be able to run IPMAT.