What is the ATI Northbridge Driver?

I have the Visiontek Theater 550 MCE video card and I'm using the latest 7.1
drivers for Vista. I noticed that there is the Catalyst driver, the Theatre
550 Pro drive and an ATI Northbridge Driver.

If I install the Northbridge driver, it causes my mouse and other USB
devices to no longer function, so I don't install it.

Is it necessary? Here is my hardware setup:

ASUS A8N-E Motherboard with nForce Ultra chipset
AMD 64 X2 4200+
2 gigs of RAM
ATI X1950 Pro PCI-E w/256MB memory
Visiontek Xtasy Theatre 550 Pro MCE
IR Blaster
250Gig Seagate Baracuda SATA II
310Gig Seagate Baracuda SATA II
NEC DVD RW 16X IDE
Floppy drive (yeah, I know!)

I just wasn't sure if the Northbridge driver was necessary or is this for
ATI chipset motherboards?

Thanks!