Mate, don't make the same mistake I did when I came here April 2010. I had the 59 day visa from their consulate in Sydney b4 I came here and thought that it kicked in after the 21 day free period. It doesn't. Its 59 days from the day you get here, so I was fined when I went to renew it for overstaying my visa.
If you come here for a period of less than 21 days you do not need a visa, but if you plan on staying longer than the 21 days and don't have the visa to cover the initial time they won't let you into the country as I understand it.
Also, something new is the one year multiple entry visa they offer now, mate of mine got it in Sydney last month, he is here now for three months. However I haven't checked his passport stamp to see if he has to renew it after 59 days here. It all gets a bit confusing. I think on my visa I only had a 3 month window to enter the country, but could be wrong so many San Mig Lights later. Can't check my passport now as their Bureau of Immigration has it for my latest extension and renewal of my card, pick it up tomorrow. (with more late fees again)

Cheers
Brett.