How to do this

[garnet]

I will encourage my customers to send invitations to friends to visit my store.

In the email there will the a link to my index page. Something like

 

www.kupuvalnik.com/index.php?somehidenfield=somevalue

 

There is a hidden field and it gets populated with the value now.

The problem is that

$igraid2 = tep_db_prepare_input($HTTP_POST_VARS['hiddenfield']);

doesnt get any value.

I want ot be able to get the value and do something with it only and when a person just visit the index page. I.e. they dont need to do anything extra.

 

Any suggestions?