NT lockup

I have a Dell Dimension XPS R450. System specifications are as follows:
Processor - Intel Pentium II 450 Mhz.
RAM - 128 MB
Video card - Creative Labs Graphics Blaster Riva TNT 16MB (AGP)
Sound cards - Creative Labs SoundBlaster AWE64 (ISA) and Turtle Beach Montego II A3D (PCI)
Modem - US Robotics 56K Voice INT PnP (ISA, *not* a WinModem)
Network adapter - Netgear FA310TX Fast Ethernet (PCI)
SCSI controller - Adaptec AHA-2940U2W (PCI)
>Attached devices - Quantum Viking II 9.1GB WLS HDD, NEC 32X MAX CD-ROM, Iomega Zip 100 internal drive
Keyboard - standard 104-key
Mouse - Logitech MouseMan Wheel (PS/2)
Monitor - Dell Trinitron 21"

I currently run MS-DOS v6.22, Windows 98 SE, Windows NT Workstation 4.0 SP5, and SuSE Linux 6.1. I have experienced a problem with system lockups in both 98 SE and NT, although only once in 98 SE. At seemingly erratic times, the entire system freezes. I am unable to use the keyboard or mouse to regain control via CTRL-ALT-DEL, forcing me to reboot.
The only known conflicts (as shown in 98 SE) are the disabled onboard IDE controller and between the two sound cards (Gameport and SoundBlaster Pro emulation). The only time the lockup has ever occurred in NT was when I updated the OEM drivers via a downloaded update from the Logitech website. Please assist me in determining the cause of this problem and possible solutions.

Best,
Copernican