I picked up a 24" Jamis Fester for a friends daughter. I couldn't find the exact model and year, but it's similar to the 2006/2007 models on Bikepedia.
It had kite string tangled and wrapped around the whole gear train, the chain was rusted, and the rear wheel would hardly spin.
I took the rear wheel and derailleur out, and removed the cassette and got all of the string out of it. The axle still didn't spin smoothly, so I took it apart, and it appeared to have water in it. Dried it out, cleaned the bearing balls, re-greased and reassembled it. Couldn't find a tool in my Park tool kit to take the cassette freewheel apart to check and re-lube it's bearings, so I squirted some oil in along the inside edges, and called it good for now.
The rear axle/cassette still makes some noise, sorta like grinding, but intermittent. It rolls great, and will keep spinning almost endlessly, but it's just not quite as smooth as our bikes. It seems to do it while pedaling and while freewheeling, so I'm not sure it's the cassette.
My questions are
Does Jamis use some different parts that require different tools than Trek, Specialized, etc?
I've been able to work on every other bike I've had in my garage with this tool kit.
Is this cassette even serviceable? Does it use a special tool other than what would be in a standard tool kit?

I'm pretty anal, and I know there are plenty of bikes rolling around with more issues than this, but I'd like to get it as perfect as possible.
I only paid $25 for this bike, and my friends are on a pretty tight budget, so I don't want to have to take it to a shop, and end up paying $50 to get it perfect.
My wife is out of town with our digital camera, otherwise I'd take some pics of the bike to explain things better.