if you're going to bromborough pc world see if they have any ex demo W7 laptops for Sale
i bought a W7 ex-demo about 4 years back cut down from £1200ish to £449 it was
it came with the box and charger and everything you would otherwise normally get but only a 6month warranty than a 12 month one which doesn't bother me tbh
nothing has gone wrong with it at all either so all is well.
(it's a HP DV7 series btw)
in relation to W8 my gf has a samsung ultrabook thing with W8 and she hates it, as do i. if you're using it touchscreen then i suppose that'll be ok as that's what it's designed for but without touchscreen it's an absolute ballache.
re swapping PC's: your mums PC is better than yours both in processor and graphics. the rest is not that much better, but it's better.
and also what little_pob said about XP, if you have vista now, downgrade to XP or upgrade to 7. vista is probably by far the worst version of windows ever. i would personally downgrate do XP (even though it's really an upgrade)