Softbox For On Camera Flash Compact, Easy To Use, Efficient Flash Setup Question?

Flash setup question? - softbox for on camera flash compact, easy to use, efficient

I have a Canon 40D and had to use a flash for my photography. I was browsing around the house the other day, and I found an old Vivitar 3500 flash. Works well with the camera, but I want the flash of the camera, use the hopefully with a light box. The flash is a PC sync connection, then what is the best solution? Thanks