No, that is desktop RAM, the iMac takes laptop RAM. Go here to find out what exact RAM you need: http://eshop.macsales.com/shop/apple/memory/iMac - don't forget to scroll down for older models.
That Mac comes with 2x1GB sticks, so in order to upgrade to 3, 4, 5 or even 6GB, you have to get 1x2GB, 2x2GB, 1x4GB (+one of the 1GB sticks you already have) or 1x2GB + 1x4GB.