how do i with a name and date of birth find out where someone was born?

This may sound like a sarcastic response, but it's not intended to be:
It depends on where the person was born.

It is possible if you know the approximate location - if it is a USA
state, then you can search the records of each county within the
state.

It would help if you explain what you are trying to accomplish or for
what purposes you want to know where someone was born.  You could pay
a private detective or an online search service $50-$100 to get that
person's address history to find out what general areas they have
lived in for most of their life.  Or a genealogist could do the same
thing.

The information is out there--you just need professional assistance to
guide you in the right direction.

SINCERELY
4keith-ga

If the person has died, you could try checking the Social Security
Death index for some answers.

http://www.ancestry.com/search/rectype/vital/ssdi/main.htm
http://ssdi.genealogy.rootsweb.com/cgi-bin/ssdi.cgi

If the person is still alive, depending on the date of birth, the
information may be harder to find. Many states will not release birth
information until a certain number of years have past.

To find out how to get birth records on individuals, try going to:

http://www.vitalrec.com/

Hope this helps!

By obtaining the subject's social security number you can ascertain
the state of issuance.  If the subject is relatively young now, it is
highly likely that the SSN was issued in the state he was born.  Its
not an exact science, but it is a step in the right direction.  From
there you can narrow down the location through vital records, if
available in that area.