I have recently begun beta testing FFXI for PC. So far I have seen only 1 summon. Summons work on MP and drain MP while they are summoned. The summon I saw was Carbunkle, a bluish fox type animal. To become a summoner you have to take your charecter to level 30 to recieve the quest for the job title. Once you have done the quest, which is in Windrust i believe, then you can start training a level 1 summoner. Hope that answers the question

Dunpiel, 10th lvl Red Mage, Beta