Girlfriend PC

So I am trying to convince my girlfriend to get some PC parts so I can build her a PC and she can play some games with me. Her favourite game is Planet Zoo so that's what we are aiming for! The budget is around £300, low I know however I have a spare 1TB HDD, EVGA 600W PSU, keyboard, mouse...

I've got a mystery-hope someone has got a clue. Motherboard with socket 775,Intel P4 3.0,915p chipset,4gb DDR2 400 memory,4MBit FWH Bios,700w power unit,NVidea graphic card and 1Tb western hard drive. They all work well together and tested on another computer. Here's the problem - I turn the...