Download: Stuffit Archive
"Epson has not released an official driver for the SP750. This driver should be the closest you can come to these days though. This is not a "native" SP750 driver, rather one that was hacked together from the Epson Stylus COLOR 740 driver. Of all the officially supported drivers, the SC740 driver seems to be closest in specs to the SP750."
model nozzles max res other res code buffer
Photo 750 48 1440 x 720 180, 360, 720 esc/p2 256K
COLOR 740 144 1440 x 720 180, 360, 720 esc/p2 256K
Most resolutions should work, but I haven't fully tested all of them. I've had nothing but positive results so far. The only down side is that the color printouts will look like they came from a SC740 rather than a SP750. They'll still look quite good, but not as good as you're used to.
Also, one big advantage this particular version of the unofficial SP750 driver has over the others is that the printer utilities work! The Epson printer utility is in the /Library/printers/Epson/Utilities folder.