Note: Installing Microsoft Windows SharePoint Services 3.0 over any beta or trial edition of Microsoft Office SharePoint Server 2007 is not supported.

Links to download the RTW versions:

Microsoft Office SharePoint Server 2007 x86 English Evaluation 

Windows SharePoint Services 3.0

Here are the Product Keys you will need when installing SharePoint Server 2007

SharePoint Server Standard Trial: XJMKW-8T7PR-76XT6-RTC8G-VVWCQ
SharePoint Server Enterprise Trial: F2JBW-4PDJC-HKXTJ-YCKRP-T2J9D 

Installation Instructions

For WSS 3.0 refer to the Windows SharePoint Services in Windows Server 2003 site for installation and deployment details.

Installation guidance on Microsoft Office SharePoint 2007 refer to the following 

• Deployment guide
• Known Issues/ReadMe articles
• Upgrading to Microsoft Office SharePoint Server 2007
• Installing Microsoft Office SharePoint Server 2007 by Bill English (SharePoint MVP)

Build to Build Upgrade Resources

• "Upgrading from Office SharePoint Server 2007 Beta 2 Technical Refresh to Release Version":
  Will be located here 11/17: http://go.microsoft.com/fwlink/?LinkId=78039
• Step by Step Instructions (with Screenshots) Office SharePoint Services B2TR to Release by Shane Young (SharePoint MVP)
• "Upgrading from Windows SharePoint Services 3.0 Beta 2 Technical Refresh to Release Version":
  Will be located here 11/17: http://go.microsoft.com/fwlink/?LinkId=78040
• "Upgrading from Office Forms Server 2007 Beta 2 Technical Refresh to Release Version": http://go.microsoft.com/fwlink/?LinkId=78041

Version to Version Upgrade & Migration

• Upgrade to SharePoint Server 2007 (IT Pro) 
• Upgrade WSS 2.0 to WSS 3.0 (IT Pro)
• CMS 2002 to SharePoint Server 2007 (Developer)

Related Resources:

• Build to Build Supportability
• Version to Version Supported Paths
• Features comparison, Edition comparison, and Differences