[UPDATE]
Standard hardware config (Athlon XP-M 2000+, 256MB PC133 CL 3-3-2-5, Geforce 4 Ti 4200) -
Forceware 41.09 + VIA 4in1 4.37, AGP Fast Writes ON, AGP set to 4x, AGP Master 1 WS enabled for both read and writes - crash to desktop at random - no error message.
Forceware 41.09 + VIA 4in1 4.56 - AGP Fast Writes ON, AGP set to 4x, AGP Master 1 WS enabled for both read and writes - crash to desktop during the first test, visual C++ Runtime error:
The attachment c error.jpg is no longer available
Forceware 45.23 + VIA 41 in 1 4.56 - AGP Fast Writes ON, AGP set to 4x, AGP Master 1 WS Disabled for both read and writes - crash to desktop during the first test, NVDD32.DLL invalid page fault:
The attachment nvdll.jpg is no longer available
Forceware 45.23 + VIA 41 in 1 4.56 - AGP Fast Writes OFF, AGP set to 4x, AGP Master 1 WS DISABLED for both read and writes - 3D Mark 01 UI flickers during tests, framerate is noticeably LOWER then with fast writes ON - about 10-15%, 20% in the High Detail tests - crash to desktop on test 4 (dragothic - high detail) - no error message
===========
Replaced CPU with an AMD Athlon (non-XP) 1200MHz - Forceware 45.23 + VIA 41 in 1 4.56 - AGP Fast Writes ON, AGP set to 4x, AGP Master 1 WS Enabled for both read and writes - 3D Mark 01 completes succesfully but scores a little over 9000 pts witch is pretty low for a Geforce 4 Ti4200. I was expecting someware in the range of 10000 pts.
==========
Put the Athlon XP-M 2000+ back in, replaced Ti4200 with a known good Geforce 4 MX460 from Leadtek - same as above - crash to desktop, no error message.
Replaced Geforce 4 MX460 with a Leadtek Geforce 3 Ti200 - again, crash to desktop, this time I got the runtime error again.
++++++++++++++++++++++++
My conclusion so far is that there is some kind of incompatibility between nvidia drivers and the VIA KT133A chipset when using faster CPUs (like my 1666MHz Athlon XP 2000+ mobile) witch nobody ever bothered to fix.
Further testing is required. I'd like to install windows XP on another hard drive and repeat the tests. Another thing I want to try is an ATi video card but as I'm away from home I don't have one at hand - apart from an 8500 all in wonder that suffered some phisical damage but might be fixable.
If the config is stable with an ATI card it confirms my nvidia drv - VIA KT133a lack of compatibility when running newer CPUs. If it's stable under XP with the Geforce 4 ti tough, it's simply a driver issue and I might be better off installing a Radeon 9500 or 9700 in this PC and calling it a day.