well if its only 9x12 like you said...150 dpi would be minimum I'd think. 300dpi is usually best, but not always necessary.
I did two sticks at that size, one at 200dpi printed at work on a $300 color printer, and the other at 300dpi printed at Kinko's, I couldn't tell the difference.
The thing to remember, is you are really talking about how high a resolution you are putting on it. If your pictures are blurry at 300dpi, its because you are taking a low rez picture and scaling it up, which is the same issue as printing it at 72dpi.
You have to find high resolution artwork, if you are dealing with low rez pics, you might as well print at 72dpi,' cause there isnt going to be a difference.