All Apple computers ship with 1 year international warranty. You can extend this to a 3 year applecare warranty anytime in the first year – before your original warranty runs out. If you are not sure if you macintosh is still under warranty, Apple keep a central record of all macs and you can check out if your computer is still under warranty by entering your mac serial number here. If you are buying a second hand mac this is a good way to check the warranty on it as well.
You can get your serial number by going to the Apple menu, About This Mac, More Info, and then you can copy the serial number from there and paste it into the Apple site.