INT = assign an IRQ to the card. VGA may limit the refresh rates to stay within VGA limits, but that's just a guess.

This page recommends enabling INT for better video card performance. Why would that make a difference?

NOTE: The AGP Video board shipped with the HP Netserver E60 has the interrupt jumper disabled. The performance of some video intensive operations, such as 3D rendering, can be improved by enabling this jumper on the video board. The AGP slot on the system board is physically connected to PCI Interrupt A, shared with slots 1 and 5. However, sharing only occurs if the jumper is removed from the card.

ETA: Here is information about the VGA jumper. Apparently disabling VGA allows the AGP card to be used as a secondary video card, presumably with a PCI card as primary. This is such an unusual arrangement that the jumper was removed completely.

ATI has no card available with a functioning VGA-disable jumper or switch. (There are several models with what appears to be a VGA-disable jumper as well as a VGA INT jumper; the VGA-disable jumper has no function or use in setting up multimonitoring on Windows 2000.) Of the displays ATI offers, only the 3D Rage Pro PCI and 3D Rage Pro AGP 2x support VGA-disabling currently. Of these two chipsets, only those supplied with SGRAM can function as VGA-disabled. You also should be sure you do not have a 3D Rage Pro Turbo chipset. These chipsets function as VGA-disabled displays, but with serious corruption; therefore, they are currently not supported as VGA-disabled displays on Windows 2000.