Your pc will need as much memory, as you can put into it. Right now I'm playing on a 192x256 map with 11 civs.
Using all the best mods I can find (including the new AAIP - great, great grafics - see the gallon, it's better done than the ship-of-line - and the javelin....) it now takes 3-4 minutes pr. turn. And I have 96 Megs.
But you can bet there are demand for it - if I don't get a 128 Meg blok as a X-mas gift, then I'll buy on myself after NewYear - that's for sure.