I am trying to redirect only one of my https pages to a http one, since i dont have ssl installed and it keeps causing error messages,
Can I do this for one of my pages, e.g. https://site.com/signin.php. to http://site.com/signin.php
Since you do not have an SSL, you will always get the warning, even with a redirect.
For the redirect, the visitor still has to visit the HTTPS page first before they can be redirected to the HTTP page.
So while you can put in a redirect, it will not cause the SSL certificate to go away.
If you have SSL support, you may want to just buy an inexpensive certificate until most of the traffic coming to that URL has stopped.
I'm not sure that Jeff is correct (but I'd feel safer about the link if it did give the warning during the redirection).
If you need to learn how to redirect, have a read of the tutorial linked in my signature and look for the coding examples (force https examples also includes force http).