how do I find someone's place of birth without them knowing!  I have a
date and their ss#.  Thanks.

It might be difficult, depending on where they were born and when.

On the other hand, it might be dead easy.

More details, please!

But please not too many details! Publishing a private individual's
Social Security Number on Google Answers is strictly forbidden, for
reasons of privacy. The same is true for any personal data, including
home addresses, birthdates, and the like.

Scriptor

With the social security number, you can narrow the search down to one state.  

You can tell where a Social Security Number was issued by the first 3
digits of the number. This tells where the person was living when the
number was issued, not born, yet it can be a valuable clue as to where
to look for additional information.

The Social Security Account Number is divided into three sets of
digits. The first 3 digits (area number)indicate the state or
territory in which the number was originally issued. The second group
of 2 digits (group number) are the order in which SSNs are issued for
a particular area. The third group of 4 digits (serial number) is
simply issued in numerical sequence.

The list of states can be found at the bottom of the following page
from Search For Ancestors.com:
http://www.searchforancestors.com/archives/ssdi.html

http://www.investigateanyoneonline.com/ssn-aboutnumbers.shtml

Thanks 
Steve