I've had quite a few partners ping me offline asking about access to the bits. We finally released the bits today as a VPC for any Dynamics partner to download via PartnerSource (requires login). PartnerSource is a portal available to partners who focus on Microsoft Dynamics and related business products.
Of course, if you are an ISV partner you should definitely contact your Partner Account Manager to ask them to invite you to join Metro. Metro is the early access program we run in Developer and Platform Evangelism. It'll get you access to the bits as well as early adopter product support and even training. The nice thing about Metro is that once you join you'll have access to all our early access products not just Dynamics.
Microsoft Dynamics CRM 4.0: Virtual PC Image - CTP3 Beta Release (Requires Login)