The Sport has Sora (meh) and the Comp has 105 components (much better). Other than that, not sure what the big price difference is- the wheels? They better be the shiznit hoops. What's interesting is the Elite has SRAM and disc brakes for less money than the Comp, but an alloy rather carbon fork. I have no experience with SRAM, so I can't compare it to the Shimano 105 group.

I own the Tricross Comp v 1.0 (2006) with 105/FSA Gossamer double and I love it. I recommend it because like other 'cross bikes you can fit fat tires AND fenders on it. Incredibly smooth on the road and can take it onto dirt, mud and rough roads and double track. I've even toured on it. The only change I've made on it is a new chain and a Brooks saddle.