Touring - Freewheel or Cassette?

You may or may not have seen that I posted a thread up a few days ago asking whether it was worth building up a Dawes Sterling I'd gotten my hands on or not. Well I've decided that I will and what I'm about to start is with the drivetrain. I want to get a new cassette but I'm not sure if it is a cassette or a freewheel... and Sheldon Brown has made sure I don't go and waste money on the wrong one before I'm sure. So do any of you guys know which it will be?
I had a look and I think that it I can see the splines on the lockring, and they turn with the sprockets when spun backwards (so it would be a cassette yeah?).... but.... it only has 6 sprockets so I wasn't sure (as from what I've read this seems quite few for a cassette).
Any ideas guy?

Rob.

Also an additional question. If it is a cassette (which I'm coming to think that it is) then can I pick whatever cassette I like and trust that it will fit?

Also an additional question. If it is a cassette (which I'm coming to think that it is) then can I pick whatever cassette I like and trust that it will fit?
The sort answer is no. Cassettes come in all different combinations and widths. If you post a bicture, someone would be able to help.

Freehubs with splined freewheels require lockings to keep the sprockets in place. The lockring has a splined inner hole (as does a freewheel) but also some rotation instructions such as
lock-->

Freewheels have no instructions and no separate lockring.

Shimano Uniglide cassettes came in 6 speeds. These had identical splines all around, so to put a modern cassette on you would also have to get a new freehub body. http://www.sheldonbrown.com/k7.html

Rats, I was hoping for a freewheel vs cassette thread...

Cheers Guys.
I have decided that I am rocking a Freehub and will upgrade to Deore XT accordingly.

Um... if it`s a casette freehub with 6 sprockets, it`s probably a Uniglide, as Andrew P mentioned, and will require some surgery to fit an XT 7 to 9 speed cassette. Not to be offensive, but if you don`t even know whether you have a freewheel or a casette on your hands, you`re going to need some help for that. There`s also the possibility that it`s a Suntour or some other type that will never accept a cassette. You might as well bring it to a bike shop now and have the mechanics check it out and explain your options. If I were you, and really wanted to get more gears on that bike, I`d probably just go the easy route and replace the rear wheel with a newer one.