There are two ways actually.
Create a path in the arc or circle of your choice select the path with your Text tool and begin typing OR while the text is selected the Text Warp T above and curve in the control pallette. (which is usually doced above the artwork.
InDesign CS, Photoshop CS, Illustrator CS, Acrobat 7
Windows XP & MAC OS X (Yes I Use Both, Not at the Same Time)