Tack,
You are in the same position we were in last year. We we got the KOP in 2007 i thought everything i needed to make the robot "run" were in the two totes we picked up. I was sadly mistaken. The first thing i noticed was that there weren't axles in the kit, i think they fixed that this year with the 1/2" aluminum shaft in the kit this year. You can do several things to attach the wheels to the frame. Drill out holes to 1/2" and slide the axles through the holes. What we did was drill out the holes to 5/8" and use a flange bearing in each hole (see pics below). Using a chain to drive the wheels is a great idea. You will need to buy a "chain break" to get the chain to the length you need. You can get one at Lowe's for ~$22.00. While you are at Lowe's get a few "master links" so you can make a loop of chain for your drive.
Here is what we did last year:
http://www.chiefdelphi.com/media/photos/27588
http://www.chiefdelphi.com/media/photos/27587
It's a 6-WD with two different chains on each side. This is not needed to get the 'bot running. As long as you can get power to at least one wheel on each side, you can get moving. You will be surprised at how awesome seeing your first robot move under its own power feels. We were cheering in the hallways the say ours moved for the first time.