You got a C2D, just not a Conroe, like Stilz said
Of course shops rip you off like that, that's what happens usually, they sell a cheaper part as if it's the latest thing. We made a big step with performance when the 2.x GHz Conroes were released, but later on Intel released a lot of budget parts that were actually inferior to AMD's processors, they just sold well because
1. They have the Intel and C2D brand (to n00bs)
2. They overclock well (to advanced users)
Anyway, you can overclock it, but you won't get any further than raising your FSB to ~285MHz, since that's where the entire stuff will just lock up, I'm on the same mobo, I just have an e4400. Just be glad you didn't get an e6300, because that one won't overclock at all, given its default 266FSB.