If you really wanna join pc gaming I highly reccomend starting with a minimum $600 budget.
There is not much you can save from those parts. The monitor, the psu (if it can handle a 9800, it must be at least decent), case and optical drive, you can also use that HDD, as a slave one. The motherboard is most likely not compatible with DDR3 memmory, those ram sticks are terrible and not compatible with new motherboards, that processor is five or six generations old and also not compatible with new motherboards, that gpu is eight or nine generations old (even though i think it can run mostly any games at medium settings yet) and runs very hot.
I am about to sell a higher spec'd machine for $100, so no, that's not a good buy in the least bit.
If you're gonna buy a used PC, at least look for one that doesn't require you to replace the motherboard once you decide to upgrade your RAM or CPU. --- 4670k | 2GB GTX 770 OC | 8GB 1600 9-9-9-24 | 120GB SSD | 1TB WD Blue | Win8.1 Pro http://i597.photobucket.com/albums/tt56/S26DG44B/PsythikViolet_Blooded.jpg