Illegal operation error messages...help!

Hi all,

I keep getting illegal operation errors with all of my programs, the error
messages appear randomly & it's driving me insane. Here's what happens most
of the time - I run MS Word (for example) and a few seconds after starting,
MS Word says an illegal operation has occurred and the program needs to
close. So I close the dialog box & MS Word closes. I then hit START to run
MS Word again and I get a message saying "kernel32 has caused an illegal
operation & needs to close"; my PC freezes and must be restarted. This
little sequence of MS Word crashing then kernel32 crashing when I hit START
happens every time MS Word crashes - without fail. The same sequence occurs
with other programs too.
This happens 4-5 times per week, sometimes 3-4 times per day. What can I do
about this? How do I stop these error messages from appearing?
My PC also randomly reboots occasionally of its own accord, any advice on
how to stop all of this?

My system specs are below, any advice is appreciated.

Thanks,.
Chris

Windows 98
Intel Pentium 4 2.0ghz CPU
765mb ddram