Yes you'll need a specific cassette (assuming cassette still). They use a different spline pattern.
Also I think you need to know what speed you hub will take, the 8 speed are longer than the 7 speed etc.. Though I presume you can spacer it out, but you'll need to know which 'click' in the shifter you should be missing as the bottom cogs are wider apart than the top cogs.
All in all, Suntour freehubs are something you need to invest in rather than just get going.
Mine went down the pan (7 speed) when a tooth snapped of the top cog and the freehub began to wobble. Not getting the cassette of means I cannot fix it
Nothing on ebay at the moment, only one on ebay.com
http://cgi.ebay.com/NOS-Suntour-PowerFl ... .m20.l1116
Not sure if you need a microdrive compatible freehub for the Microdrive cassette (the 11 tooth)
If it's not Microdrive then it will just be the bottom cog that is screwed on.
But don't go buying modern suntour cassettes
If you're a freewheel I think it's easier.
As a side note, this is the same method Shimano used for pre-Hyperglide (& hence lockring) cassettes.
Also note there is a APIII cassette that is Shimano spaced, which I think comes under the PowerFlo 'Rear' branding.
