I think I have both of those cards. I have the -57 one in a rig. It has 512 Mb DDR3. The-56, still in the box, has 512 Mb DDR2. The DDR3 version has a Molex plug - the 4-pin (like for fans and your HD), not the 6-pin on some of the new beefier power supplies. The DDR2 version does not have a power plug.
SPECS ON NEWEGG.COMYou need two cards of the same kind, so your second card would need to be the same as the first. The DDR2 box says it's SLI ready. Haven't opened it and it still has those two plastic bands around them and I don't have anything to cut them with and it would mean I would have to get up off my couch to go look for a sharp tool. I'm not even watching TV because the remote is just out of reach on the floor.
If you need me to get up to open the box let me know. Maybe I'll get the remote at the same time.
God I'm a lazy fuck.
EDIT: Click on the two pics and enlarge the ones showing the blowup of the card. The -57 shows the SLI connection contacts on top. I don't see any on the -56. If it is SLI ready as the box says, I don't see how you could connect them. You should be more like Cantrip.
Twitchy: "I pulled a Cantrip . . ."
GivePeaceAChance: "If the Tempest had nipples, I'd pinch that shit."
Xylicon: "I'm about to deliver my [Richard] in your face for posting that stupid shit. "
WDF?: "He keeps reaming me... night after night... I'm rather sore."
GivePeaceAChance: "OMG MY NIPS ARE HARD"
llenta: "cantrip, you fail!!!"
Filliam H. Muffman: "i'm on top of dick"