I think i can give the best reference to this question.
My currently working configuration:
AMD Sempron 2800+
512 MB ram burned out to 256 MB Ram (biggest pain)
Nvidia GeForce FX Go 5200 64MB
The game as such is running very nicely, at medium detail level, @1024x768
However due to the small ram, I tend to play small or standard size games. At 512 MB ram, with 10 AIs, i experienced a little lag, this was however more due to the number of calculations the game needed to make.
After my ram went defective, the game turned different, I still play at same resolution, but most detail levels were lowered to low. Early game is still ok, but even mid game turns to be insanely long taking.
The current game that i am playing (playing as amurites, advanced start, standard map, 13 AIs, epic speed) is more like a game of chess rather than a turn based strategy. 5 turns per hour. However, its not like its unplayable, its just that it needs to check for all the functions, since im in late game, and 10 of the 13 AIs are my vassals.
As overall, its not so bad to play FFH on a laptop (15'' display btw), if you dont need all the fancy gfx.
RAM however is the most important thing this game needs. As you can read on many sites over the internet, CIV4 is not very optimized against memory leaks. And FFH needs even more processor and RAM resources due to so many functions. Although i was surprised that the thaw function, hasnt affected the gameplay very much even at 256 MB ram.
I wouldnt really recommend going lower than 1GB of ram for smooth gameplay experience, however i am the living proof, that you can run (i dont say its comfortably playable beyond mid game) CIV at a much lower configuration.
Good luck with the bidding
