you need to buy it through the GFWL client, but seems to work....
10p for a full game, plus 2 expansions aint bad
Amazon price £22.91
(apologies if i did sometihng wrong here - first deal)
i'm not sure when it ends though!
Can also be purchased for 10MS points for those with Xbox Live accounts and not wanting to use a credit card
PLEASE DON'T EXPIRE BEFORE 6AM ON MONDAY 22ND - the deal is valid until then but occasionally the website throws up a price of £27.49. If it does, delete basket & try again via http://www.gamesforwindows.com/en-GB/dailydeal/day7/
The CD key can be found on the Games for Windows Marketplace application that you used to download the game from.
CD keys have temporarily ran out, you can still buy it and download it, you will have to wait a week or two to be assigned a key.http://forums.gamesforwindows.com/t/15693.aspx