Default sound device problem

I recently installed VOIP software for a bluetooth headset on my PC. I'm
running Windows XP SP3.

After installing the software, the default audio device switched to 'imFONE
USB Audio', instead of 'SB Live! Wave Device' which came with my system. I
was told by the VOIP headset company that this was why my system lost all
sounds, and advised to change my default audio device back to the system
device.

I went into Sounds and Audio Device Properties, Audio, Sound playback
Default device: and selected 'SB Live! Wave Device' and then clicked 'Apply'
then 'OK'. This fixed the system sounds and all my system and application
sounds work normally, until I shut down my system for the night.

The next time I start up my computer, the system sounds continue to work,
but all application sounds are not working. When I checked in the Sounds and
Audio Devices Propoerties, Audio, Sound playback Default Device is reset to
'imFONE USB Audio' again. After selecting 'SB Live! Wave Device' as the
default, all application sounds start working again.

But, after shut down and startup again, the application sounds do not work
and I have to go in and reselect the system audio device as the default again.

Is there something else I should change in order to keep the original system
audio device as the default?

Thanks so much for your help!
Cyndi