Is there an online video converter?
How old of a Mac? MPEG Streamclip is a great option.


  This free software requires at least Mac OS X 10.2 (Jaguar) and QuickTime 6. It is also compatible with Mac OS X 10.3.x (Panther), Mac OS X 10.4.x (Tiger), Mac OS X 10.5.x (Leopard), Mac OS X 10.6.x (Snow Leopard), OS X Lion, and QuickTime 7. It works with PowerPC and Intel based Macs.


Unless you are living the the Stone Age and have a Mac running 10.1 or lower, you'll be fine. 

You can batch convert files by going to List>Batch List:



You'll be presented with a screen like this:



You can add files from there and convert them.