Can i put a vivitar film flash on a nikon DSLR?

I have a film camera, really old and it has an okay flash and i was just wondering if i could put that on my nikon d90?

I would say this. Compare the bottom of the flash - the contacts - then look at your nikon and compare the connections. You'll probably find that there's a major difference. If these don't match the flash won't work properly, if at all.

Older flashes tend to have higher voltage than present-day models and may fry your nice camera's innards.
Is it worth the risk?

I would not do it without using something like a Wein SafeSync http://www.bhphotovideo.com/...oe_to.html Older flashes can have a flash sync voltage of 150+ volts, whereas most new DSLRs are around 6 volts. Using the older flash on a DSLR without a regulator you can fry the cameras control boards.