Apple released iTunes 7.6 which updates iTunes to support movie rentals. Both the Mac and Windows versions get the same update description.
Rent and download your favorite movies with iTunes on your computer or directly to your living room on Apple TV. Enjoy rented movies in sizes up to 720p HD with surround sound on your Apple TV and sizes up to DVD-quality on your computer. Transfer your rented movies from iTunes to your iPod or iPhone and enjoy them on the go.
It’s available through Apple software update or as direct downloads for Mac and Windows.Rentals weren’t available yet, at least for me, even though I appear to meet the requirements (iTunes 7.6 & in the US with US credit card).
Even if I clicked on one of the “top rentals” my only option was to buy it. Oh well. [Updated Jan 16th: There’s a movie rentals button on movies today and lots of rental tiles around the iTunes story.]