as someine who has owned both pc and mac, i think you’re making the right choice re the macbook. you could always turn your mac into a pc freindly machine but there are cheaper ways of achieving the same result – buy a pc.
as far as that goes – just go to pc world/comet/curry’s with a clear idea of exactly what your system requirements are and then buy a named, branded machine that meets the criteria.
as for the ‘saturday boy’ – not half as bad as the pushy assistant mananger, desperately fighting his way up the greasy pole – just tell him what you want, stick to it and talk over him abruptly if he tries any sales spiel or sucks in through his teeth at your suggestions.