To change from ACPI to APM, you don't need to delete your partitions1. What to do instead is:
- Back up your data (just in case)
- Boot off the windows 2000 cd, pressing F5 when it prompts about raid controllers
- Select 'Standard PC'
- Choose to do an upgrade install2 on the partition windows 2000 is currently installed on.
- Optionally, disable the ACPI device in the BIOS.
- Reapply any service packs.3
The reason you have to run setup again, rather than just changing the hardware abstraction layer in device manager is that windows NTs depend on a device heirarchy stored in the registry to be able to boot properly. Changing from ACPI to APM so drastically alters the machine that the stored heirarchy often does not correspond to the actual hardware to a sufficient extent for the machine to boot. Windows 2000 can recreate the tree once it boots, but if it can't do that the install is rendered unusable. Running setup recreates the device heirarchy from scratch, so the machine is guaranteed to boot properly. Changing the HAL in device manager can render your machine unbootable, or worse.
A better solution than switching to APM is to get rid of your old hardware/software. As long as the device works, there's no reason to be concerned about it sharing IRQs. If your software is so old that it tries to drive the device directly instead of through windows, your problems are just going to get worse when you upgrade your operating system, as each successive version of windows is more strict on direct device access. Programs that are written to use the APIs instead of the hardware will work well into the future. (For example, telemate talks directly to dos com ports, and can't use a winmodem, even in windows. Hyperterminal predates the winmodem, but works with it anyway, as it talks to the windows API, and the hardware differences are hidden from it.)
1 - If you really want to delete all your partitions, you can do that by booting from the windows 2000 setup CD, rather than messing about with windows 98 boot disks.
2 - Windows XP calls this a repair install, but don't confuse it with the 'press R to reapir an install' option on the first menu.
3 - If you are installing off a CD with the service pack slipstreamed, you can omit this step.