Windows 98 randomly hangs

I have a customer who runs a testing program to test his employees with, and Windows randomly hangs during the operation of this program. The machine has 192 MB of RAM, has been defragged regularly, and all TEMP files have been removed. The latest patches for Windows have been downloaded as well. Still hangs randomly. The software vendor claims that it is a hardware problem, although I can’t find anything wrong with the hardware or the OS. Any suggestions would be greatly appreciated. Thanks