If it were me, I would get something newer. Those Sony systems are obsolete and are surely out of warranty by now (unless you've got a very good deal!). You cannot upgrade the motherboards in them either, so you would be locked into slow and pre-owned hardware. The slowest Haswell CPU's (Intel's current gen. processors) are faster than anything the Sonys can take. If building systems is new to you then I only recommending hardware with a warranty, because components, old and new (especially old ones bought on the internet) can arrive D.O.A. from time to time. I would also suggest that the GPU is actually a much lower priority than CPU/RAM/HDD and even power supply because most modern CPU's have decent graphics processors built in. A quality power supply can be crucial for stability, plus the more components you add then the higher the power it will need to provide. Do some research on features such as RAID, memory speeds, CPU benchmarks and GPU benchmarks if you plan to play 3D games or use GPU supported* video applications. If the budget is tight, take a look at AMD components. If you can afford Intel components, then they are very robust and usually use less power for faster processing speeds. Its all about preference, really, and what you aim to do. Google is your friend in this case, you just need to ensure that you get a motherboard that will take your CPU, get RAM that is of a compatible speed and that you get a case that it all fits in. The other components should be pretty universal.
* GPU really isn't that important for video processing unless you're using commercial tools with a supported graphics chip to do real-time video effects rendering using certain plugins. In other words, if you just want to capture and process video with AviSynth, a fast GPU will actually make no difference.