If it weren't for the fact I'm utterly terrible at Civ, I'd be up for it.

It's one of those games where, as much as I enjoy the gameplay, I've just never mastered it.
I'm hopeless at the game myself - anything above Chieftain level seems to be beyond me.

I still love it, though.
My problem always is that I never have as big an army as I thought I did, so if I don't have any technological advantage, the AI's huge stacks always kick my ass.
The thing with Civ4 I find is to focus on a few goals, not all, tailored to your civilization. Playing as the Mongols, I prefer to focus on technology and take advantage of the early special unit to crush my enemies, see them driven before me, and hear the lamentations etc. (even though it's pretty useless as a city raider) rather than focus on religion or culture based city improvements in particular (just enough to get by, I guess). This was a departure from how I played as the Germans, for instance, which was essentially building and researching and develoiping Wonders as quickly as possible, while maintaining a decent army.
On the other hand, getting a few more units than your immediate enemies by the first few 60-80 turns of the game always helped me by the time war is necessary, especially as you can choose who to crush, and I often find I can wipe out a fair few enemies quickly, if inefficiently.
Variety is the way to conquest too - using a wide variety of attack units means you'll have a suitable counter to those axeman-killers or those horsemen-killers who whip your arse each time. Units causing bombardment or collateral damage in particular are your friend, and not just for city raiding either.
When I play Civ 4, whenever I get pulled into a war (or, more often than not, whenever I choose to start a war

), I think "What would Churchill do?" and essentially drop everything and drive every city towards a war footing (even if it means changing civics to Serfism and Theocracy), producing as many armed units of whatever variety as possible. It usually works (especially using the Dougie Haig strategy of "sending all your young men to their doom"

), and often I end up with a few spare.
I remember once an enemy AI declared war on me on the lowest setting. Bastards sent over a huge stack of galleons and ground troops.

Fortunately I had discovered airships and old-style fighter aircraft by that time.

Still, it took me by surprise and I did lose one city. (Got it back, though.

)