Measure the frame's dropout like Bill mentioned above to see if you need 120 mm or 126 mm spacing. The frame can be "cold set" (bent) to accommodate a different size if need be, but ideally we'll find you something that matches the original.

I may even have a set out in the garage I could give away. If I do, you can have 'em for the price of postage and a decent six-pack. (Almost certainly under $50 total.) My fiancee will thank you for helping me clear out a little more room in the garage.