There's only one board I know of that can pair a pentium 4 socket 478 (which the 2.4GHz is) with PCIe and that's the Biostar P4M900. I'm going to assume you don't have that and that you're asking about an AGP card. If so, don't waste the money on a 9500GT (which doesn't even come in AGP) or a 4650 as a 2.4GHz P4 won't come anywhere near using either one of them. Your best bet is an HD3650 or an nvidia 6600GT (if you can find one). That said, there's an open box HD3850 on NewEgg right now for the same price as an HD3650
Yeah, a 3850 AGP card, while nice (for AGP) would still be bottlenecked by this processor.
Not to mention that the value of a 2.4 P4 is debatable (I upgraded my friends Socket478 motherboard to a 3.2 processor for $19.95).
And it would be hard to recommend an upgraded P4 and an AGP video card. It would still be slow AND the cost would be too high.
Like the last post said, save your money and buy something better.