Thanks Aaron ... Yes, I agree with you. A fresh graduate should only have a vague idea about his/her fields of interest, and I think Grad schools acknowledge that. I think the professors look for future potential rather than past accomplishment (which is a factor, but not the principle one). And they should be able to see whether the applicant is being sincere or not.
As far as I am concerned, i have finished Masters, and have a relatively clear idea about what field I want to explore. However, I'm also open to other fields of study provided there are good facilities available. Should I mention that to the prof? Or should I keep things strictly under his own area of research?