@BCLG: PP is good (yeah our site admin too), but aside from akots's comments, I really think the Taj Mahal should not be underestimated this game. Don't forget that it actually counts double, you get a GA, plus the enemy does not. 1+1 = 2 GAs for one Taj Mahal. Decent logic, isn't it?
@akots: they're not that retarded btw, both have music, and only need nationalism, gunpowder and mil. tradition themselves too for cavs (don't forget they have their research output combined since about turn 20). Or alternatively, they can put up good defenses with gunpowder and chemistry -> grenadier, since they already have engineering. They absolutely can't be underestimated that's for sure.
Also, 20 turns...? I personally don't believe this game can be decided so fast, but we shall see what happens. Don't forget that I have to earn money myself inbetween bursts of research, so after 4 turns for Liberalism there will have to be a small period where money is generated too.
Research after Liberalism really still has to be decided upon, that's the good thing of civ4... lots and lots of possibilities.