A GPU (graphics processing unit) is often, but not always, synonymous with a video card, aka graphics card. The GPU is actually on the video card. In lower end systems, and most laptops, the GPU is part of the main system board, and in some newer systems like AMDs APUs, the CPU and GPU are the same chip.
The 8800 is an older card, with a 700Mhz GPU and 512mb of GDDR3 memory, while the GTX 750 Ti is newer with a 1Ghz GPU and 2GB of GDDR5 memory. Based on that alone, the GTX 750 Ti is the better graphics card. But can your system handle the newer one?