Is this installing from a disk? If it is, download Impulse from http://www.impulsedriven.com and log in with your current forum account. Click on the Impulse orb in the top left and select Register a product. Put in the serial # on the back of the manual.
This will allow you to re-download the latest game version at any time with no limits, so you don't have to bother with the disk.
You will need Impulse anyway to update the game, and there have been so many patches since the release that your patch download size will only be slightly smaller than the full patched game.
