How to open a external php file by clicking on a movieclip?

Okay, here’s the thing:

I have a php file (a guestbook for on a website)
In flash on the timeline, I made a movieclip, and I want the php file to pop up (the guestbook) whenever you click on that movieclip.

I have no idea what code I have to use.

The php file is in the same folder as the .fla file.

Thanks in advance,

-Edwin