Give this a try. All you need to do is check to see if you are on page X and then redirect to page Y. Consider RewriteCond statements to be 'if' statements.
If you need more redirects just duplicate the last two lines and edit the paths.
You have to check the query string for the value in the "pid" variable and then redirect if the value in that variable matches a page you want to redirect. You can do this with the "RewriteCond" and "RewriteRule" directives like this.