Popup javascript on PHP page after confirmation

Hello, I am new and am looking for assistance making a popup box after submission of confirmed order. I am using an open source online store script. I won't name the name unless I'm allowed to.

Basically our customer has asked to add a popup on confirmation which advises his shoppers they are entitled to a free t-shirt if their order exceeds $40. It then advises they email to the store email address their receipt as proof.

The code is all php on the page. I am able to get this to work

Code:

---

echo "<script type='text/javascript'>alert('Really annoying pop-up!');</script>";

---

but it doesn't let me add additional text or html for "mailto" reference.

Any help is greatly appreciated. Thank you

This one can be deleted. For some reason after I submitted the first time it didn't show up, so I posted again. Sorry for messaging twice.