You have a few options. Modern road wheels are spaced at 130 mm, whereas mountain bike wheels are spaced at 135 mm. If you cold set your Nishiki to 130 mm for a modern road wheel then the rest of your drive train probably should be updated to accommodate an 8,9,10, or 11 speed rear cog set. That will be a big and potentially expensive overhaul.
I'm assuming your Nishiki is a 6 or 7 speed rear cluster. Simplest fix is true or rehab your current rear wheel. Another option is buy a similar used rear wheel in good shape. Feel free to post details and/or pics of the bike and we can give you some more specific advice.
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N = '96 Colnago C40, '04 Wilier Alpe D'Huez, '10 Colnago EPS, '85 Merckx Pro, '89 Merckx Century, '86 Tommasini Professional, '04 Teschner Aero FX Pro, '05 Alan Carbon Cross, '86 De Rosa Professional, '95 Gios Compact Pro, '95 Carrera Zeus, ‘81 Masi Gran Criterium, ‘81 Merckx Pro, ‘89 Cinelli Supercorsa, ‘83 Bianchi Specialissima, ‘VO Randonneur, Ritchey Breakaway Steel, Rivendell Rambouillet, Heron Randonneur, ‘92 Ciöcc Columbus EL