Is there a way to round the corners of the Rectangle Marquee Tool? I'm trying to figure out a way to create a mask of a rounded-corner rectangle with 8-radius corners.
#1
Use the Rounded Rectangle Tool from the tool palette. Once you click on it, enter the amount of curve you want in the options bar, and decide paths or shape layer - I'd choose paths, then load the path as a selection from the button at the bottom of the paths palette.
#2
In Image ready there is a rounded rectangle marquee tool. However in Photoshop as YrbkMgr said the rounded rectangle tool is the way to go.
#3