The "Jasper" revision, which runs cooler thanks to microchip size shrinkages was released around August last year, so it's unlikely that this unit you're considering is such one.
I have a Jasper myself, they're supposedly RRoD-proof, but really, no one knows yet. They might just take longer to break!
The only way you can tell them apart is on the power label on the back. It MUST say "12.1A" which basically means the unit has a 12.1A rating on it's 12V rail. Older units have higher ratings, such a 15A. I went into Gamestation and asked if I could look at their boxes. If you peep through the hole in an Xbox360 carton, you can see the current rating on it. I just kept asking around until I found one... though it did raise a few eyebrows!