I recently upgraded from a K6-III/450 on an EPOX EP-MVP3C to a Thunderbird 850 on an MSI K7T Pro-2A. I was going to do a fresh installation of Win98SE, but decided to see how it would act on boot-up. It just redetected the chipset and updated drivers and ran with no problems.
I don't know what chipsets you have, so results may vary. Hang on for a while and see what other people recommend.
Friends don't let friends install Windows ME