I got Entrenchment today thru the Paypal thingy, and I was puzzled for a while about why it wasn;t showing up in impulse.
Anyway when I checked my email it said that if you use paypal, and your paypal account email doesnt match your impulse registration email, it doesnt automatically transfer across.
Anyway beneath that it gave instructions:
If your software does not show up automatically, you are logging in with a
different email address than above. You can register your serial number
manually by following these steps:
1) Go to the registrations area of Impulse by clicking the question mark near
the top right corner and selecting "Register a product with Impulse?".
2) Click the "Add Registration" button at the bottom of the window.
A. Copy and paste your serial number into the Serial Number field.
B. Enter the email address you used to place your order, as shown above.
C. If the Product Category and Product do not automatically change to the
correct product, change them as necessary.
D. Click "Add Registration".
3) Impulse should now display your software under the My Games or
My Software tab.
4) Select your software from the list and an Install button will appear in the
bottom right corner. Click Install and follow the prompts.
5) Impulse will download all the necessary files and install them to your hard
drive. Once this process is complete, click Run to launch the software or
use your Windows Start Menu as you would for any other application.
I did the above and it worked for me afterwards - Hope it helps you too!