Try the following:

1. First makes ure that ACPI is enabled in your BIOS settings. Some systems force you to turn it on, some don't. Best to check and make sure though.
2. Next go to IBMs web site and download the ACPI support drivers for Windows Me. I have attached a link and some info to where I think you need to go.

http://www.pc.ibm.com/support?lang=en_US&page=brand&brand=IBM+ThinkPad

Choose ThinkPad A21m from the Family option and then, after the refresh, type acpi in the search window in the *upper-left* part of the screen. On the list of choices thjat comes up, I believe the one you want to use is Upgrading To Windows ME From Windows 98. In the next list that pops up choose IBM PM Device Driver Fopr Windows ME. In this document you will find the driver files you neeed and installation instructions. Hope this points you in the right direction.