If you had SharePoint Server 2007 Beta 2 and it expired. Then check out this post by the SharePoint Team Blog.

Upgrading from an Expired SharePoint Server Beta 2 Trial

Upgrading from an Expired SharePoint Server Beta 2 Trial

1. Perform a complete Server and SQL backup of the SharePoint databases.
2. If at all possible follow the “How to install the Beta 2 Technical Refresh update in a new installation” instructions to install Beta2TR on a different server. (Note: You will need to have access to the Beta2 installation bits to do this. We are working on making the bits available. More to come later.)
3. If an additional server is not available, if you have the beta 2 bits, you will need to uninstall and follow the rest of the steps in step 2.
4. Follow the steps to setup the new farm for the first time (setup services on server, create SSP, etc) then attach the Beta 2 content database to force an upgrade on the content.
5. Start planning the Beta 2 TR to RTM upgrade as Beta 2 TR will expire on May 15th. (See Beta 2 TR Resources below)

Beta 2 to Beta 2 TR Key Resources:

• Installing Microsoft Office SharePoint Server 2007 for Beta 2 Technical Refresh
• Download: SharePoint Server 2007 Beta 2 Technical Refresh
• Microsoft Windows Workflow Foundation Runtime Components Beta 2.2 and Visual Studio 2005 Extensions for Windows Workflow Foundation Beta 2.2
• Microsoft .NET Framework 3.0 Redistributable Package
• Microsoft Pre-Release Software Microsoft .NET Framework 3.0 - Release Candidate

For more resources check out the Running SharePoint Server 2007 Beta 2 and Encountered Expiration?