I completed the Resistance campaign on my old PII 400. All the settings were turned pretty much down to mimium and it wasn't especially pretty .... occasionally I even had to find a good spot, pause the game, put the viewdistance up so I could have a look around and then put the viewdistance back down so I could keep playing.
Your setup should be sufficient, but you will have to play with the Options a bit.
OFPEC is strictly an editing site so we don't do general technical support like this.... but we like to try and help people in that brief interval before the thread is locked.
The best place for your question is over at the Official forums
www.flashpoint1985.com. A moderator will be along soon to lock this thread. Even better lock it yourself by clicking the green solve button.
Welcome to the magical world of OFP! You'll be back here soon with mission editing questions, I guarantee it.