Simply download this achievement world and place the pumpkin on top of the 4 iron blocks, to create an iron golem.
https://www.dropbox.com/sh/68ihnr8ivz3jstw/AAC4bPQToqc06k9hk...Note: Since update 1.4, you will need to use shears on the Pumpkin first before placing them on the iron golem!