Release of WSS RTW and MOSS Standard and Enterprise Edition

YOu can download the Release-To-Web version of WSS (Windows SharePoint Services) and Microsoft Office SharePoint Server 2007 Evaluation version at

1. Microsoft Office SharePoint Server 2007 x86 English Evaluation
2. Windows SharePoint Services 3.0

CD Keys available for standard and enterprise edition are

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

For more resources about installation, upgrade, versioning, check this link, from Microsoft SharePoint Products and Technologies Team Blog