I don't know if this has been posted before This is not a game/Beta but you can sign up for beta testing games. Beta Info Sign Up Instructions for joining the Beta Program: Go tohttp://connect.microsoft.com. You will need to sign in using a valid Windows Live ID and register on Connect if you have not already done so. Click the Directory link near the top right corner of the screen. Click the Entertainment link in the list on the left. Click Apply under Your Status for Microsoft Game Studios Beta Program. Complete the application questionnaire.
Have you ever got in a beta from that? Ive been signed up for around 5 years and have never got in to any game betas, although I have got in to the Office 2003 and Windows Vista betas in the past.