ok guys I thought as much. You need to manually clear it out of your registry... A pain I know but it works. When your skrewing with this if you don't follow directions to the t its your fault it you comp ends up with problems not me... 
ok her it goes
unistall game and all complonents then go to your registry via : Start-> run, and type regedit
look for:
HKEY_LOCAL_MACHINE\SOFTWARE\Stardock\Drengin.net\sins
HKEY_LOCAL_MACHINE\SOFTWARE\Stardock\Drengin.net\sinsentrench
or For Vista 64 bit;
HKLM>SOFTWARE>Wow6432Node>Stardock>Drengin.net>sins
HKLM>SOFTWARE>Wow6432Node>Stardock>Drengin.net>sinsentrench
and delete both and reboot your PC and go back to Impulse and try installing the base game.
OH and thanks to "highlander" froma nother forum make sure to have 1.13 version and test it out before then installing entrenchment stuffs. Apparently there are a few who had problems when not updating befroe installing entrenchment!
This aught to do the trick! Worked for me and I had the same problem with BF 2142 and this got it up and going as well... oh EA and constant bugs of install reinstall and remove to play...