Could be VGA. That's a quite common interface for a projector (it's seen by the PC as a monitor).
So it seems you need a USB-VGA converter (comes with the necessary driver).
Something like http://www.amazon.com/Multi-Monitor-External-Adapter-Graphic/dp/B000J4MT5Q
Or you need to run the application that you want to show on the projector on a device (laptop, PC) that does have a VGA-port. Might be cheaper if they happen to have one available.
got HP TouchSmart 7320 desktop Pc at school need to connect it to the projector but dont know what type of cables should i use?!
the projector cable is 15 pins cable
the PC has a usb port
running winodws 7