Unsecure image, only https images allowed: http://img193.imageshack.us/img193/9416/imag0801v.jpg I have no idea what kind of tool it'd take to get this off. It's a cheap 7 speed Sun Race cassette. It looks like it might fit a cross looking tool into the gaps on the shiny outside ring. The ring on the inside looks like a standard cassette remover (one that would work with say, a SRAM) would fit inside it but I don't thing that has anything to do with the cassette. Anybody have an ideas? Thanks.
Looks like you need one of those Cassette removers but with a thin Hex-shape in order for it to slip between that ring of metal circling the hex-bolt. You know the removers, with those pins sticking in the middle..... There's no other clues on show, looking at that pic...
You want a freewheel removal tool like this one: Unsecure image, only https images allowed: http://sheldonbrown.com/harris/images/tl7203.jpgIf you no longer need the freewheel then you could clamp it in a vice very strongly and rotate the wheel to remove it. Sheldon Brown has a good guide on this. http://sheldonbrown.com/freewheels.html
You want a freewheel removal tool like this one: Unsecure image, only https images allowed: http://sheldonbrown.com/harris/images/tl7203.jpgIf you no longer need the freewheel then you could clamp it in a vice very strongly and rotate the wheel to remove it. Sheldon Brown has a good guide on this. http://sheldonbrown.com/freewheels.html
Sheldon's website actually shows that for his cassette with 4 teeth, he'd need the TLP23 FR-3tool : http://sheldonbrown.com/harris/tools/freewheel.html#allen (see the Sun Tour 4 prong one)