ArcGIS 9.2 Beta testers can log into the ESRI Beta site and download ArcGIS Explorer Beta 1. When you log in you should see a new area for ArcGIS Explorer downloads.
Note, the Public Beta will not be till at least March (I would assume the Business Partner Conference would be a good guess) as has been reported before. This is just a closed beta for ESRI ArcGIS 9.2 beta testers