On 9th January 1998, Microsoft announced the Windows 98 Consumer Beta Preview Program. This let “computer-savvy” Windows 95 (1995) users try out the Beta 3 build of the new OS. A “select list” of users were invited by email & could join the Program for $29.95 plus shipping/tax.
Windows XP build 2210, from 2nd March 2000, is the earliest available build of a 64-bit edition of Windows. Designed for DEC Alpha, it predated Intel Itanium & x86-64, which XP would eventually support. Its boot screen is notably just Windows 2000’s with “64” crudely spray painted on top.