You are in luck. If the rear dropout spacing is 130mm (or very close to it) then pretty much any current rear wheel will fit in there. With a bike of that age, all kinds of modifications could been done over the years. Look carefully at the current rear wheel. If there is a 4 mm spacer behind the 7 speed cassette, your current wheels are compatible for as many as 10 speed cassettes. If you are willing to upgrade, and your current wheel can accept(possibly depending on whether there is a spacer behind the cassette), you have many upgrade options