Paul Thurrott over at Windows IT Pro reports that the first beta of Windows Longhorn is planned for July 27

According to my sources at Microsoft, the software giant has set its sights on July 27, 2005 as the release date for Longhorn Beta 1, though obviously that date could slip if the company is unable to hit internal bug requirements. The current escrow build for Longhorn Beta 1 is 5101, a few builds older than build 5103, the current internal build in the Beta 1 fork.

Exclusive: Longhorn Beta 1 Schedule Revealed