Strange. VC should remember what voice you select when you save options... It will only get confused if you add / remove voices from windows.
to set the default TTS voice in windows 32 bit is easy.
Go to VC options
go to system tab
click TTS settings
select default voice.
if you have windows 64 bit the 32 bit voices may not show up. Then you need to use another method.
run the following
C:\Windows\SysWOW64\Speech\SpeechUX\sapi.cpl