Unfortunately there's no "single" way to turn on Antialiasing for renders.

Do you run Mental Ray, Maya Software, Maya hardware, or a third party renderer?

Note: If you didn't touch the button to RIGHT of the "IPR" button, then chances are you're on Maya Software.

Click on the button to the RIGHT of IPR -- that's "render globals" IE: Options for Rendering.

On the popup, click the tab marked "Maya Software".

Near the top there'll be a menu -- "AntiAliasing Quality" on "Edge Antialiasing" dropdown menu click "Highest Quality" Under "number of samples" set that higher too (8-16 is uber quality, can go up to 32 though that tends to BLUR things, not just antialias... 4 is decent for quality + speed of render).

Multipixel filtering will also help you a bit... but forget it generally... too complicated.

To start out in your adventures for Antialiasing --> Just click the dropdown menu to highest quality... leave everything else alone... it should work nicely.