Currently Being ModeratedJul 7, 2013 1:28 AM (in response to YT1000)
Hi @YT1000, and welcome to Apple Support Communities.
In order to watch your purchased movies on your iMac, you will need to open iTunes on your iMac, go to Store, from the right-hand set of links, click on Purchased, then from the next page click on the Movies tab, pick the movie which you'd like to watch, and click on the iCloud icon (with the down arrow inside).
I hope that helps. Let us know if you have further questions.