Originally Posted by TrackSmart

The wheel he linked to was aluminum (not steel), so that's not an issue. Also, the small difference in dish between normal 6 and 7 speed wheels would be unlikely to be a problem. Even older derailleurs should be able to handle the difference without a problem.

However, if he has 120mm spacing (older-generation 5-speeds), then things are different. He'll have to "spring" the rear chainstays open a little bit to use these wheels, which are spaced for 126mm dropouts. Not a big deal, really, but he may not have enough clearance to run a 7-speed. He might still be able to run a 6-speed, but it's not guaranteed either, UNLESS, he got one of the more rare skinny 6-speed clusters they used to make, which fit in 120mm frames (check ebay for suntour ultra 6 speeds I think).

Edit: lots of suntour ultra 6 freewheels are on ebay it seems