How to find compatable cassette for older Shimano
Take your rear wheel off and visually inspect the cassette.   Compare with this answer https://bicycles.stackexchange.com/a/21406/19705  and see which  you have.

Given bikepedia says 8 speed, its most likely to be a cassette.



This is a freehub with a cassette.   Note the ring of indentations just inside where it says 12T.  That silver ring will unscrew and all the cogs can slide off.



By comparison,this is a freewheel.  If you undid the black lock ring then the guts of the freewheel will still be on the wheel.



Image credits to Sheldon Brown's website http://sheldonbrown.com/free-k7.html