Voiding the warantee on one is no problem. My old Etower 366 was voided a week after we bought it when Nat'l Semiconductor Corp quit the business (they made the Cyrix M2 processor inside). Just open the damn thing up and do whatever you want; if I may suggest something, get a new processor fan. Mine sounded like a diesel engine until the day it finally flew apart in a cloud of shrapnel.
I think you misunderstood. He doesn't care about opening it up, him mother cares.
Tales of processor fans exploding are only going to increase her unease.
I really just don't understand why someone would want Windows 98 instead of XP.
Maybe she doesn't want to surrender her free will to the corporate hegemony of a monopolistic monolith of a software company's paranoid control grab under the guise of 'Product Activation.'
Or maybe she thinks the "X" makes it sound 'naughty.'