This is a weird situation with my Presario 5284. I assumed the machine had ACPI, though turning on detection in Windows 98 through the registry yielded no new devices, and no way to Suspend besides what APM offers (CPU fan off, hard drive spins down, PSU still on). The BIOS has no options for ACPI, but has a single power management toggle for APM.

Now onto the disgusting BIOS, which I couldn't open with any normal tools, be it Phoenix, AMI, Award, etc. It turns out it's some kind of malformed Phoenix BIOS, and Phoedeco disassembles it into several files which are attached below. (256kb file is the full ROM) When 90000000.dec is opened in a hex editor, it shows the standard BIOS options, as well as... an ACPI tab! But it's hidden in normal usage. Going further down the file reveals a DSDT for the system, which confirms that it's not just a menu left in by accident.

The only problem is that I'm not sure how to re-enable that menu, and with it ACPI. I tried all kinds of keyboard combos to maybe unlock the hidden menus, such as FN+tab, ctrl-alt-basically every key on the keyboard, ctrl-every key, but nothing changed. If this were a normal Pheonix BIOS, I'd be able to put it into Phoenix BIOS editor Pro and re-enable the hidden stuff, but the original ROM file and the disassembled files don't open at all. Perhaps there's some kind of other software to do this?

Any input would be greatly appreciated.