The Beta Program was more limited, Milestone Releases were widely released and MSDN had access to specific builds. But this is the largest program to date. It used to be:I stand corrected. Were they available to the wider public of just MSDN subscribers etc?
ALPHA Builds - Windows Internal and Select Microsoft Employees with limited Partner (OEM Driver teams mostly)
BETA 1 - Closed Beta by nomination
BETA 2 - Wider and some Public Builds
Release Candidates - Public Availability