Hey there, Im about to convert my Trekk 4300 frame into a single speed. I plan on getting the Surly Singleator to tension the chain. As for the rear, can I use a cassete orshould I use a freewheel? I'm thinking the freewheel will work better as the cassette will ahve more rooom, allowing the chain to fall off. Also, for the front, can I just take off the outer and smalle ring and put spacers on the chainrings? Also, is a 32 in front and 16 in rear a good gear combo? I hear that for singlespeeds it should be a 2:1 ratio.

well, the ratio 2:1 is a good marker, but ride to YOUR ability. You know what that is after a few spins on the SS Rig.
You can use your exist rear wheel with a 'splined' cog (like those on your cassette) and some spacers, or just get a SS-specific rear wheel...your call.

Once you pay for all the spacers you are half way to a cheap threaded hub. i woul get a single specific hub or find and build up an old freewheel hub. 2-1 is not a bad start but be ready to get another freewheel.
NOTE: Make sure the freewheel uses the four dog removal tool. The two point tool is getting more rare all the time and is not nearly as strong.

around these parts, spacers can be had for just a little begging at the LBS. Nothing's cheaper than free.

Free? They wholesale for $1.50 each. Must not be the owner handing them out.

I believe that you will need a new crankset, I have a 2002 Trek 4300 and the chainrings are riveted together, if you have the crappy Suntour crankset still on it. As far as I can see you would be better off without those Suntour cranks anyway.

They are probably scrounged from the junk box - busting up old cassettes is the easiest way to get them.

Another alternative is PVC pipe. Get a piece w/ an inside diameter exactly the same as the diameter of your freehub body. Cut in a miter box to get a right angle. I've got my beater SS set up like this, works fine.

The pvc is a good idea. I used to use it to preload my moto forks, holds up really well. But I never considered it for cassette spacer.

I can't take credit for it, dug it up somewhere on the net. I'm still partial to the old cassette spacers, but I've run out giving them to other people when I was converting them.