Open the program SAPI Config located in the folder Haptek Player in your start menu. Run this after installing any voice to make sure the 3D engine is aware of it.
Also the AT&T voices include both a SAPI 4 and SAPI 5 version of each voice. SAPI 4 works with the 2d characters, SAPI 5 with the 3D characters. Make sure to choose the SAPI 5 version of the voice in Hal's options.