FIXED... READ!
Did some research because Im haveing the same problem. Mini dump.
I have:
Vista 64
GeForce 9800GX2
4GB Ram
3.0GHz AMDX2 Dual Core
HT OMEGA Striker 7.1 Audio Card
I figured out what my problem was and probably most of yours.
1. Installed SINS with the physical copy of the CD. (NOT DOWNLOAD)
2. Purchased SINS: Entrenchment over Impulse, downloaded then installed via Impulse.
If this is you, and the game is crashing on boot, you must do this to fix.
1. Open Impulse and click the MY GAMES tab.
2. Uninstall SINS: Entrenchment.
3. Open Add Remove Programs in Control Panel (XP) or Programs and Features (Vista).
4. Uninstall SINS
5. Open Impulse and and click the MY GAMES tab.
6. Download and install SINS.
7. Download and install SINS: Entrenchment.
Done... It works. It appears that physcial copy of the game is not compatible with the downloaded expansion pack. No hotfixes or any junk like that. Post if this works for you.