exactly. you could just take of the derailleurs, shorten the chain and wrap the chain around the little chainring and the cog it lines up with in the back(this is what i'd recommend for folks unfamiliar with truing wheels). like so:



if you do this make sure the chain is straight! if it's not it will fall off when you're cranking up a hill.

but if you're going to do the singlespeed conversion that's described by sheldon brown et al, you'll need washers (or axle spacers) NOT freehub spacers like the numerous "singlespeed spacer" kits sold by performance, surly, etc.

if that part is confusing, read up on the difference between freewheel hubs and freehubs.