http://maps.google.co.uk/
punch in ealing broadway, and the roads to the north of gordon road tend to be the best place to find parking, bt they aer a bit narrow so make sure the wing mirrors are folded in otherwise they tend to not be there when you get back

for driving

there are 2 olympia's, one at earls court and one a little ways up in kensington, easy to get mixed up

my suggestion?
drive to the outskirts of london, ealing is a good bet, find somewhere to park that isn't residents parking, walk to the tube station, get a travel card for teh weekend (if they want to go all over the place, but it's cheaper anyway) and then tube it in

don't get a london cab because they are well pricey, don't get on a bus without the travel card or a prepay'd ticket as they are nearly as bad, keep all sorts of vauluable stuff out of sight and not in handbags and stuff, even though we like to say it won't happen, there is always the risk

the tube things doesn't work to well if you have loads of luggage