The card requires 2 6pin PCIe power cables. If you don't have them you need to use the 4pin MOLEX to pcie adapter, or buy a new powersupply.
If you ahve no PCIe connectors there is a solid chance your PSU is not sufficient, check that it will provide enough power and be careful when using asdapters that you distribute them over the correct rails (if yuo cannot distribute them correctly you will need a new PSU).
The 4pin conector is either a molex (there are adapters for them) or if you are refering to the motherboard 4pin connection (looks like a pcie connector) that is for the motherboard only, not the PCIe.
Are the PCIe connectors white? I see two white connectors and one black that looks exactly the same as the white ones. The only difference is that the black one is turned upside down. The 4pin connector is a molex. Can I split that 4-pin into two 6-pins plug them into the graphics card and make it work?
You cant split a 4pin into a 6pin, you can get an adapter to turn 2 of them into a 6pin though. For this card you will need 4 free molex if you want to use adapters. Be damn sure you ahve enough powr though, I'd also like to see your psu specs to be sure.
The colour of the PCIe conenctors are not always standard. Mine happen to be red but more often than not they are black.
Here is a link for what the various conectors look like:
i have the same graphics card and would be looking to crossfire it except i have the same worry about using molex to pci-e power. i have this power supply antec trupower 650 it wasn't cheap, i paid 128.99 for it when i bought it back in 2007. im using the 2 pci-e cables it has already for the 1 hd 4890, i would need to use 4 molex for a second 4890. would this be safe to do?