Oh no, I'm sure you can put 98 on the 486, it will just be a boat anchor. I put 98 on a pentium 1 (200 MHz) computer with 128 mb ram. Frustratingly slow without 98 Lite.
I think vista will require the i686 instruction set. No pentium pro, no pentium I.
Plus, I'm willing to guess that the
Vista CD doesn't come with a boot floppy, so you can't put it on any computer that doesnt' support boot from CD.