iis 6.0: Setting Expires header don't work + cache control

Programmer Question

Hi !
from all the articles i read it seems that setting the Expires http header is very easy.
i went to the wanted directories(with iis6.0)-->right click-->Http headers--> Enable expires and setting the period-->OK

that should do the work, i thought...
but when i test my page again with PageSpeed and other tools its teling me that there was no effect on the Expiry header, altough it did add another header which i entered in the same time (cache-control : public).
am i missing a step? maybe a change in the metabase.xml file?

another question: when i checked the headers it showed me that there two conflicting headers:
cache-control:public (which i put) and cache-control:private (which i didnt put!!!)
how can i find how to take this header off? when i check the iis->file->headers i see only the one i put and not the other...

any help would be appriciated!
Liran

Find the answer here