check the passenger side floor board is it wet? Normally when the heater core leaks it will run more to the passenger side also do you smell antifreeze (if any is installed)? Also check inside you hood on the passenger side firewall there is a drain tube about half way down is anything coming out there?
If it is your heater core leaking you will over heat when the water drains out (imagine that

) It is about a 8 - 12 hour job to replace it yourself also. Here is a link to a quick article we did that shows you how to bypass it until you can get it done yourself or by a professional.
Heatercore Bypass SN95