Lock up Problems

Problem: Frequent Lock Up in IE6 while scrolling window, typically while using mouse buttons. Have two kinds of mice, one is Intellimouse and the other normal, sftwr & drivers current.
The problem occurs on two separate systems. Have new cable modem through new router, have isolated the systems off network direct to cable modem and still have problem. Cable vendor verifies all is well.
One system has Win Me, with EPOX 8KTA2 MB and Duron 700 Mhz with 256K Ram and MSI MS-StarForce 816 GeForce2MX.
Second system has Wind98, with EPOX 8KTA2 MB and Duron 650 Mhz with 256K Ram and NVIDIA RIVA TNT2 Model 64

IRQ’s seem Ok. Power Questionable, but installed battery backed up full time surge protection by Beldon (ReSource 450). Virus does not seem to be the cause. Uncertain as to whether NICs may be causing problem. Need further ideas to consider in troubleshooting, please!