100MHz fsb parts and especially slot1 100MHz fsb parts have always held a nice price premium over the 133MHz fsb parts.
why?
simply because there is (or was) tons of people like you looking to upgrade their systems, but could not run the 133MHz fsb, and didnt want to change their motherboards, or cant, because they run a compaq like you or whatever.
also 100MHz fsb p3's are likeable by overclockers as well, who have the capability of running 133MHz fsb, but buy the 100MHz part. an infamous example would be the pIII 700E (100) -> pIII 933EB (133). another example of this would be the celeron(II) 566 (66) -> 850 (100). the main goal of this is to be able to have a faster processor for less, and being less dependant on the motherboard(chipset), ram, and of course throwing the pci/agp bus out of sync (this was before they had pci/agp locks).
your board does not support tualatins, if i was you i would scrap the system, or make a new system if you crave more performance. a p3 700 with 256mb of ram still holds it's own today; it will make a nice email/web computer.
my father runs on a 800EB with 256MB pc133. it serves him just fine for what he needs - email, web, office, music, and a little p2p on the side.
edited: for math