I have to admit, I have the onboard LAN, AC97,LPT and COM disabled in my BIOS. So I don't know if the W98 would have any problem without installing 4in1 drivers if I had everything enabled, but I turn off anything I don't use.
I just wanted to write that when installing 4in1 drivers as the first software after installing the OS itself, the AGP texture acceleration was disabled and unavailable. When I installed the 4in1 package after forceware drivers were installed, the acceleration switched on and can be turned off - before the button was inactive.
Of course, I don't know if this will help solve the buggy problem every time, but I haven't had a chance to get any older versions of the BIOS (the oldest version is from 2006), changing the speed of the AGP (8x to 4x) hasn't helped, and other tips on the solution haven't worked either. The procedure described above solved the problem in my case.