Passing variables between pages

Hi, I want to pass a variable between three pages. I tried to get a username from the first page through a form. Use that username in a select statement in the second page to query a table.Everything is fine up to that point. now I want to pass the same username to the third page where I have to use it to select a table name by that username and it doesn't work. I tried $_POST['username'] and the value is not passed to the third page. Is there a way of doing this? Please help. Thank You. Rashini