How to disable ISIS driver

I'm attempting to use some TWAIN compliant software on a computer that was
previously using an ISIS driver. The computer is Win 98, 2nd edition. The
scanner is a Xerox DocuImage 620S. I got the driver
here:http://www.altoimaging.com/AltoWeb/...ductSupport.htm

I have installed the driver but whenever I attempt to use it with a TWAIN
compliant software I get the following error messages.

"Scanner scsi communication fault"

"Can not start xtw620.exe. Please close other applications then retry the
TWAIN session"

"Out of memory, not enough memory for the TWAIN device. Close other programs
and try again."

It says in the driver readme file "Note: Do not attempt to open the TWAIN
driver if you already have the DocuImage Scan Tool, Scanner Support or ISIS
driver software open, or vice versa".

My application that uses the ISIS driver is still working so I assume the
ISIS driver is still loading and grabbing control of the scanner.

I would like to disable this ISIS driver but have not been successful.
Anything I do I would like to be able to undo. I have tried doing a
step-by-step configuration boot to see if I could avoid loading this driver
bit I didn't see anything applicable.

Could someone offer any advice on disabling this ISIS driver.

Thanks