totally awful at computers so if what i say is way off go easy on me
i just bought a xfx geforce gts 250 1gb video card, computer meets all the requirements except my power supply only had 250W (needs at least 450W) so i took the 480W i had in my other computer..now both power supplys didnt have pci-e but the geforce came with a 6 pin pci-e cable, would that work? copy/pasting what one site said....
"If your power supply doesn't have a 6 pin PCI Express cable then you can use the adapter to convert two 4 pin peripheral cables into a PCI Express cable."
depends on the PSU, check how much current it can deliver on the 12V rails, there should be a sticker on the side of the PSU. If its an older PSU most of its power will not be on the 12V rail like a modern one. Post what it says on the sticker on the side, PSU wattage doesnt mean much and the actual abilities of a PSU at a rated wattage vary a lot.
Only 1 item labeled +12V? If so then you only have about 192W of power available on the 12V rail, all of the power that the graphics card draws will be from the 12V rail, the GTS250 has a TDP of 145W, that doesnt leave much power left for any of the other components that need power from that rail like hard drives, fans or the motherboard and CPU if its a newer design. I wouldnt use the molex to PCI-E connector you risk blowing your PSU.
You should probably upgrade to a good high quality 550W unit that you will be able to hang onto for many years, a good 550W with ~40A on the 12V rail will power any single video card. The corsair 550VX is a common recommendation, yes it seems expensive but its one of the few parts that you wont need to upgrade in the next 5-8 years.