What CPU do you have? There's no such thing as a 1.2 GHz P4. The slowest P4 made was the 1.3 GHz Willamette model. (Which performed about as well as a 933 MHz P3, but that's not the issue here...)
The 9700 Pro is a great card, but if you really do have a 1.4 GHz P4 or something close you're really spending more money than you need to unless you plan on moving it to a faster system at some point.
I'd probably recommend something like a 9500 Pro, which can be found for well under $200. If, however, you can find a 9700 Pro for under $250 I'd probably get it. (I've heard that Best Buy has offered rebates on them recently, which makes them a relatively good buy.)