Passing vars between functions (with POSTs)

Hi, I'm struggling to pass from 3 functions (and one of them have a html form POST) one simple variable called $login. Once in the function (that have form with POST) is calling a php3 without passing the $login (like: common.php3&login='someone') and since the next function doesn't have any relation with this one (doesn't receive any value by return) but requires the same variable ($login). My question and great doubt is: How can I share $login in several functions... without use or change (because I don't have access) the PHP configuration environment... I believe that this could be solve with register_globals var but I don't know how to do it. Best Regards, Miguel