Wow, yes that is more than enough. I should have clicked on the link first (from your post I thought you meant it had only a 19A and a 18A rail, which would have been close). So from there, P=IV so Imax combined is 600W/12V or 50amps, plenty for a GTX260. Sorry for the confusion. I hope you enjoy your new card.
You should be fine with that power supply as long as it has the required pci-e power connectors.
750 watt is lots although I would go with a better manufacturer like CORSAIR, PC POWER AND COOLING or ENNERMAX EARTHWATTS.
But that's my 2 cents....still should do the job ok!.....