You can find on your Photoshop install disk a .iff plug in. It will allow you to open the .iff file directly into Photoshop.
Just render out the .iff, open Photoshop, then just open the .iff directly into Photoshop with the transparency. Once in Photoshop you can save it anyway you like. Post any problems & version Photoshop if it's not working. Good Luck