I'm a long time Civ player but have never played multiplayer game. I'm about to change that.

Few questions first:

What civs are good to take in a multiplayer game and what ones to avoid?

Same question for wonders and buildings.

Well, when choosing a civ for multiplayer you are generaly going to want one that a) has a UU that will be useful during the eras the game will take place and b) is Financial. If you obey these precepts you won't go wrong.

Assuming an Anceint Age start I'd say the best multiplayer leaders are:

Mansa Musa(Mali): He has the Financial trait and the Spiritual trait (which is decent). Also, they have Skirmishers, which are an amazing UU that requires no resource, and is availible very early on. Skirmishers are great for either saving your ass while you hook your resources up, or for early rushes, especialy on small maps. I would argue that Skirmishers are the best overall UU in Civ4 multiplayer, but that's a topic for another thread.

Quin Shi Huang(China): He's Financial and Industrious, which is pretty great for games with isolated starts where you intend to build wonders. Also, his UU is pretty decent and stays useful as a siege weapon for a long time after regular Crossbows become obsolete.

Huayna Capac(Inca): He's got Financial and Aggressive, which is a great multiplayer combo. Also, he gets Quechuas which are pretty useful for screwing around with an unprepared opponent in the early game. Also, that Agressive trait means that with a Barracks you can pump out Axemen with an extra +25% bonus against melee units. These super-pumped Axemen will cause major trouble for an opponent that isn't Agressive as well, especialy if he doesn't have Horse Archers.

As for wonders and buildings, it's pretty much the same deal as in single player. The only thing you have to remember is to be careful about investing in wonders too heavily at the expense of your millitary/expansion, cause you might get clobbered.