Although we can download Leaked version of Windows 7 Pre beta through torrent,but without an activation key, you can only use it up to 30 days trial.
It was found that the old Windows Vista Beta and RC product keys can be used for Windows 7 Pre-Beta which can activate it,but those keys are limited to activate up to 10 copies installed on a Pc.
But I Googled one article which share us list of 15 Multiple Activation Product Keys that you can use to activate your Windows 7 Pre beta both 32-bit and 64-bit editions.
These are the activation keys
These Activation keys can be used unlimited times in unlimited different client PC.
these keys are no longer working i have tried them all, the only way to install is install the trial verson i.e without putting the windows key in. and then keep using the rearm command to extand the trial.