Separate threads are made in the games section for each item being auctioned. The maximum bid is 200 or 250 (I don't really remember) points above the last bid, so you can't go from 100 points to 6000.
You can bid on 2 items, but you can only win 1. If you win both, you or the FO team will choose which one you win. The other item goes to the bidder who placed his/her last bid just before you did.
In some cases they may need your snail mail address to send you the item you've won, so keep that in mind when you start bidding on something.
I hope this helps.