You can now download full version of games via the newly launched Games for Windows Games on Demand service. You can see the complete list of games now available here. Once you download the Games for Windows client, be sure and grab Tinker. This is a free game that will allow you to add some new achievements and couple of hundred points on to your Gamerscore for free and while you are sitting at your desk.
Download the Games for Windows client here, then once you install it you can download Tinker from within the Games for Windows LIVE application.
If you need some help in Tinker, we’ve got you covered here.