Here's how you tell what version you have:
-hold the case in front of you and look at the case
-Make sure there is good lighting so you can see well
-examine the color of the case
-if it's white you have a V1.0
-it it's not white you're not holding a 360
There is only one version/generation of the Xbox 360 so far, it's the version everyone has. There may be slight variations in some of the internal components, like the DVD drive, or memory brands, but those things do not define a new version or generation of the console.
If someone tell you they have a "2nd Gen" or "3rd Gen" Xbox 360 they're either ignorant or lying. There's no version that works better then another version... THERE IS JUST ONE VERSION; some work some don't.
When a new version of the hardware DOES surface, expect to see it on the XS news page, and this topic will be updated on how to tell.
Ummmmmmm......... I seem to be holding up a green halo 3 xbox 360. Not white, but is it still a 360? Hmmmmmmmmmmmmmmmmm..................... Maaaaaaaaaaaaaaaaaaaaaybe...... Still a one and only version numero uno, but colored different. Juuuuust had to be politically correct. Unless me eyes deceiveth, and china sold me a faulty 360. Nope, you're just an idiot. I thought it was sooooooo important to tell you this, I just had to sign up to tell you. I feel better. Oh, and the fact that the elite DOES have better a cooling system AND an update already on it means it's slightly better than it's even crappier predecessor.