cannot get dsl service

[wile033]

Hello and thanks for any help you can provide me with (actually this is my son's problem... I'm just trying to help him out). Several years ago (2001 or 02) he went to an apple store and bought a brand new IMac. At that time, the very first 'flat-panel' design had just hit the shelves, but after ogling that for a while, he chose the more affordable IMac g3 600 which was (and is) more than adequate for his needs which are mostly music, photos, e-mail, web browsing etc. Well, it proved to be a good choice as it gave him great service for the next couple of years. Then he had some job changes and was moving around, so he was forced to put his imac in storage for a few years. Last month, he once again settled down in a permanent location, so he took the imac out of storage, booted it up, and it seems to be working as good as new...so he called to get dsl service. They (at&t) sent him the usual stuff...the splitters, cd and modem etc. and he hooked everything up...but when he tries to register it...he cannot ...and the tech support at at&t told him it's because he has an old version of internet explorer (4.5 i think) and to get dsl you need at least version 5.5. About eighteen months ago, concerned about routine updates, I took it out of storage briefly, just to update explorer...and at that time I was unable to do that...the error message I got at the time was because it still had...(and still 'has')...the original 2001 os...10.1.5...and to simply update explorer...it (the os) would need updates (which, even then, were no longer available for 'cheetah') Anyway...to sum it up...all my son wants ...is to get on-line. Can he just purchase a newer version of Os X and pop it in the cd/rom and get online? Can he jump from "cheetah" 'any' of the newer versions...and if so...which ones? Thanks.