EVERY graphics card has a GPU. Without a GPU, it's not a graphics card. Also, every Nvidia card since the 8000 series has had CUDA capabilities. It will also say CUDA capable in the specs if it has CUDA capabilities. The GTS 250 wouldn't be able to perform nearly to its peak, because a system that old would be bottlenecked by other things than the graphics card if you replaced it. PCIe is PCI express, and I'm not sure if the 240 or 250 would run on anything less than PCIe 2.0. x16 is unimportant in this context, they will run on anything down to x4.
PS: There's an edit button for a reason. Please don't double post within a reasonable time period, like a day or so. Just edit your previous post if nobody has responded yet.