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I'm going to assume a couple of things here...
1) This is a part of some kind of form that goes on a website, like an order form or something.
2) After they fill out the form, they click "Submit" or "Order" or whatever.
3) The PHP script will take over and process it from there...
If those three assumptions can be made, then you can accomplish it very simply by extracting it from the $HTTP_POST_VARS array when you pass it to the PHP script.
I am still a little bit of a noob at PHP, so if I am wrong on this one, please let me know...