Hi!

It has the original SCSI drive installed. (About 4 GB)

Do you know what SCSI controller the system features? Is it onboard or in an
expansion slot?

SCSI adapters that I'm familiar with generally have their own boot BIOS and
may not even show up to the system BIOS and its boot list. Make sure your
SCSI adapter or integrated chipset has its boot BIOS enabled and then remove
the IDE hard disk from the BIOS boot list. The SCSI adapter or chipset needs
to be allowed to let its BIOS initialize and take over the boot process.
With the main BIOS finding an IDE hard disk in the system and in the boot
list, the SCSI adapter never gets a chance to do that.

Can anybody help me force the box to boot from the SCSI drive?

Turning off the hard disk choice in the BIOS should do it, as long as the
SCSI adapter's boot BIOS is enabled.

What is the maximum IDE drive size supported and how can in increase
it?

A lot depends upon when the system was produced. If it was made sometime
around the early 2000s it could have a few different limits...up to about
2002 would probably have a limit at 137GB.

Sometimes obtaining and flashing to the latest available BIOS for your
system will allow you to use bigger hard drives.

William