sorry, I was thinking of Startup Disk in 9.1...
Are you saying that in OS X's Startup Disk Pane you cannot select your 9.1 system?
If so, is your 9.1 system visible but you simply cannot select it or is it not even listed as an option? If it is listed and you cannot select it, try Klink's suggestion re: logging in with the name and pw you used to setup the machine, etc.
Otherwise... Off the top of my head... What kind of volumes do you have attached to your machine? I have seen the Startup Disk Pane take 'forever' looking for available systems on multiple and/or slower drives- this can make it seem like you cannot select a startup disk until it finishes its search at which point you can select whatever you want.
Also, have you tried holding down the option key while booting? This should allow you to select your boot OS. While this doesn't fix any problem you may or may not have with the Startup Disk Pane, it will allow you to get into 9 in the meantime.
Let me know if this helps. Maybe, Grab a screenshot of your Startup Disk Pane and send it to me or post here...