Seeing as how the next build hasn't been released yet, at least to my knowledge, it's no surprise Impulse isn't registering it for you.
Given my timezone, it's close to 5 AM when I'm writing this... So, I'd guess another 24-36 hours before release, and that's only if they are, in fact, releasing the new build tomorrow. (As far as I'm aware, nothing has been confirmed by any of the Stardock staff, but they seem to have a habit of releasing the new builds on Thursdays.)
Once they do, new pre-orders, (Like you and I irongamer,) should get access to the Beta and Serial Keys, if they're still doing that. If they are, it's my understanding it'll show up in your E-mail along with the Beta showing up in your Impulse Application.
If you want to double check, make sure your Impulse settings are set to show "Pre-release Versions" using the Blue Icon in the top-left corner area. (It looks like a list-box with a drop-down arrow next to it.) And, of course, check the spam/trash folder in your E-Mail.