I'm trying to upgrade to W2K from W98SE but when I install from cd, I get blue screen message that says acpi.sys is corrupted and I have to revert to using 98SE. I've tried getting help from Gateway but they say they can only support my original OS. Can anyone help? I'm not a tecchie but can follow instructions. I've tried pressing F7, it makes no difference.

You may not like this answer but I suggest that you install a second HDrive in the system. Partition it using the correct version of Fdisk and then install Win2000 on that drive. That way you still have Win98 and Gateway to fall back on. If done properly you should end up with a windows boot menu on each boot. If you want to be able to access any files on the second drive you will need to format it using FAT32. If you perform the format from within Win98 you should be able to use a drive size of up to 120GB, if the Motherboard supports it. You can check with Gateway for info on maximum drive size in your machine.

It's not that I don't like it, it just sounds a bit extreme. Can anyone explain what it means for a BIOS to not be acpi.sys compliant? I don't even know what a BIOS is, but is it possible that my equipment can't run acpi.sys?

Look here for an explanation on acpi. http://www.acpi.info/. I recommend you install a second drive because you have Win98 up and running. Upgrading isn't the best way to install a different Operating System. You BIOS may simply have a setting disabled that could allow you to install Win2000. I still feel you would be better off to do a DUAL boot. You would be able to use either Win98 or Win2000.