Well, it depends on a multitude of variables. The first being how well the first 17 picks go.
Remember, we can't force a team to trade with us so that we can trade down. A team has to want to trade up for some reason.
So the first precondition is that a team wants to trade up. There has to be some value there that they really, really want, and that usually entails a player falling.
What could that be? It is unlikely that anyone is going to trade up for anything other than the "elite" skill positions: QB, RB, CB, WR.
I don't think a team will trade up for OT, LB, DE, TE, S because the value isn't there due to the depth. There aren't going to be any players there at those positions that are worth jumping up for and giving away another pick.
So some potential things I see: Cutler, LenDale White, Santonio Holmes, Jimmy Williams fall to us. I can envision a scenario where a team really would like to get up there and snatch up any other those players who have a "drop off" to the next person at their position. Realistically, I think it would have to be Cutler or Holmes.
Holmes is the clear-cut top WR, and a team might be willing to jump up and get him---teams like the Broncos, Bears or Jaguars.
Cutler is the #3 and there is a drop off after him. If he falls to us at 18, I think the Bears might be willing to jump up and get him to make sure a team like, say, the Bucs don't get him.
So, to trade down, the draft has to fall in a way where a player slides to us that a team below us wants to trade up for them.
If that happens, how much we get is probably defined by those pick value charts. If we trade down into the late first, we might get a 1st and a 2nd because the 2nd round pick will be late too and therefore not much of a value. I think, realistically, we could trade down and pick up a 3rd or 4th.
Based on your draft position and the way board is deep but with few stars at the 18th pick, I don't see us trading down unless someone falls to us.