Your Machine should have a PCI-e video slot and not an AGP slot, so that 6800 wouldn't work in your Dell.
The 6800 (it was available as AGP and PCI-e) will run BF2 but unless you are getting that series of card for free, I wouldn't bother since it is so slow compared to current cards.
I know for a fact that BF2 works great on these cards, 8800GT, 9800GT, GTX 260, GTX 275, GTX 285.
In America, these cards sell for $100 to $400.
The GTX models might require you to upgrade your power supply in your Dell, but normal ATX power supplies won't fit into some Dell cases without modifying the case a little.