This is a very odd problem, and it goes like this...

I'll boot up my cpu into win98se, and it'll start up fine. I'll use it for a while, then, at some point i'll have to reboot, but once i reboot and get to the logon screen, a few things may happen...

1) I will get a windows error in programs like USER.EXE, KRNL386.EXE, and BROWSEUI.DLL

2) I will get a blue screen with a VxD error.

if neither one appears immidieatly at logon, it will appear right after logon

I will always be forced to reboot either way from these errors, and they will be waiting for me again when I reboot.

The only way it seems to avoid these errors (and here's the odd part) is to turn off the cpu and let it sit for about 2 hours. When I come back and boot, it starts fine, and the cycle begins again.

I have..

AMD Duron 800MHz
IWILL KV200-R with VIA Apollo KT133 chipset
C-Media onboard sound card
nVidia GeForce4 MX 440
Realtek NIC card
256 SDRAM

any help would be appreciated
-Mike

Well I had this problem very long ago... Didn't use Win98 for years but this was caused by a bad motherboard driver...
Update all of your drivers. You might also check your ACPI settings in the BIOS setup. This issue can be resolved with better drivers I already had it.
And you only need to turn off your CPU for about 10 seconds really. The hardware is long dead by then... If it's not the case, you should check the temperature inside the case too...

what all drivers does that include? I have sound updated, what else?

also, what kind of ACPI settings? Sorry, I'm not the best with BIOS outside of its security parameters.

If you need to turn off your machine for like 2 hrs before it can boot again i would say that something in your computer is overheating.

The two possibility are either CPU or PSU.

Check and make sure all the fans are working properly and it's clean, sometimes excessive dust can cause components to overheat.

If the components are operating in a overheated condition for prolong period of time then these two components may starts to fail (not completely but enough to make the system unstable.)

Next if everything is clean and fans are ok then try to update the following things:

1. Latest BIOS
2. VIA 4-in-1 driver
3. Nvidia video driver
4. realtek driver

I would suggest that you to upgrade to windows 2000 or windows xp, as 9x series are relatively old OS and your system are capably of supporting these newer OSes.