Looks like a uniglide freehub. If you look at it straight-on from the back of the bike, are all the cog to cog spacers the same diameter?
The hub won't be any good to you for a fixed gear, it does not have the threading for a cog. You could use it for a single speed with a spacer kit but using the small cog as the lock ring. You can use a cup and cone BB lock ring instead of the small cog if you have one.
To remove the cogs you need two chainwhips. Hold the larger cogs with one while you unscrew the smallest cog with the other.
http://www.sheldonbrown.com/k7.html#uniglide