While the ideal of Mahayana Buddhism is that of becoming a bodhisattva and postponing the entry to Nirvana until all sentient beings have been redeemed, in Theravada Buddhism the goal is either to become an Arahant or, in very rare cases a Buddha (e.g., Maitreya).
This write-up is about becoming a Buddha as viewed by the Theravadins. According to Theravada, while most Buddhists of their school aspire to become Arahants, occasionally a person decides to become a Buddha. Such a person has a much harder task ahead because he must first qualify for Arahantship but renounce it, and thus become a bodhisatta. To do that, the prospective bodhisatta must meet ten prerequisites, namely:
I do not feel qualified to elaborate further (since I follow a Mahayana path). However, I refer anyone interested in more detail to http://members.tripod.com/arahan/the_buddha.html - this is not the actual link, but under Windows if you press your left mouse button and move the mouse, you can highlight it, then press ^c to copy it to the clipboard, and finally paste it to the location window with a ^v.