The motherboard you've choosen is fine and won't hinder the cards performance, However I think the Processor will be the limiting factor in games that are very CPU intensive like Battlefield bad company 2. Still I think you'll get decent frame rates in almost all games with fairly good in game settings.
The OP has a s775 CPU, as he/she mentioned previously and made no mention of upgrading.
@OP if you intend to add another GTS450 for SLI then I would recommend Buying a P55 or X58 setup, as your current CPU would hinder the performance of GTS450 SLI and I would not recommend you spend alot of money on old technology (s775)
Yes you are right, he said core 2 duo i can’t believe i missed that, assuming he has ddr2 memory and don't want to spend a lot the only choice that will boost his performance is a x48 motherboard with the card he is talking about and is really hard to find in stock somewhere in a ddr2 combo.
Look for ASUS Rampage or Ga-X48-DQ6 if they have them in stock somewere take it.
I did found a ga-x48-dq6 in a stock house only for 30 euros for a friend of mine i assume if you search deep enough you will make the dream machine reality. I did spend hours and many phone calls to find it here in greece.