I suggest staying away from that PC, unless you want it only for general use - office applications and browsing the internet.
According to the specs you linked:
"The rp5700 supports normal (or non-reversed) layout (Advanced Digital Display 2) adapter cards inserted into the SDVO (Serial Digital Video Output) connector on the system board. This connector has the physical appearance of a PCIe- x16 connector; however, conventional PCIe cards are not supported in this connector."
Thus it will not take any current PCIe video cards. I have no idea what an ADD2 card is. And it looks like it does not even have a standard PCI slot for old video cards - which are about 3 generations back.
Further it only has a 240w power supply - not enough to support even low end cards, and the CPU could be:
"Intel Core2 Duo Processor E7400 (2.80-GHz, 3-MB L2 cache, 1066-MHz FSB)
Intel Core2 Duo Processor E6400 (2.13-GHz, 2-MB L2 cache, 1066-MHz FSB)
Intel Pentium Dual-Core Processor E2160 (1.80-GHz, 1-MB L2 cache, 800-MHz FSB)
Intel Celeron Processor 440 (2-GHz, 512-KB L2 cache, 800-MHz FSB)"
Looks like this was intended for office use.