You actually don't need the dev build anymore -- the dev build is currently the same build as the live build, since the day before ISBoxer 38 went live

If you have an earlier build of ISBoxer 38, Rift wasn't yet in the list of games in the first drop-down box in the Quick Setup Wizard, or in the Virtual File Wizard. The most current build of 38 is from Feb 16, 2011, so any fresh downloads since then are the latest version

To add Rift to Inner Space (for use in the Game and Game Profile fields in the wizard), select Add Game from the Inner Space menu. Point it at riftpatchbeta.exe in your Rift folder, with no parameters necessary. Once the game is released, an actual detection will be added to Inner Space.