I know the tank question has already been answered to the OP's satisfaction but just wanted to add a bit more info.
In FFXI when you have a party to kill mobs or do events, every member of that party usually has a specific role. Roles may include healing support, general support to enhance the abilities of others in the party or impair the abilities of the enemy (buff and debuff), damage dealing (physical or magical) etc. In a balanced party, 1 person's job is to hold the attention of the enemy so that the enemy does not attack party members who are more vulnerable. That job needs two things - great defensive abilities and the ability to draw hate from the enemy. The work "tank" is used because as a metaphor, it fits - think of the massive armor.
Defense can be supplied in one of 2 ways. There is "blood tanking" where the tank is just good at soaking up hits with great defense. The best blood tank is a Paladin because they have the best defensive skills and gear available to them. Paladins grab and hold hate using many of their specific skills and abilities, including the ability to heal themselves and others, flash, bash, etc as well as abilities from their sub job, usually Warrior for provoke. They also have access to a lot of enmity + gear. Hate is also generated by doing damage but a Pld is generally not the best damage dealer.
The second type of tanking is "blink tanking" where the tank is good at surviving because they don't get hit. This is done through high evasion skill and Utsusemi - shadows that absorb hits. The best blink tank is a Ninja. Ninjas generate hate using subjob skills such as warrior provoke, same as a Pld, plus abilities and spells from the job. Using the ninja spells generates hate very effectively, as well as throwing shuriken (not done often because of cost). Ninjas can also be very good damage dealers which also helps to generate hate.
Edited, Jan 6th 2008 10:00am by Lokithor