[CR]difference in frames for double vs. triple crank

Hi all, What are the differences in a frame (if any) that have a double or triple crankset?

Living here in Colorado along the "foothills", not being as young as I used to be, blah blah blah, I find bikes with triples to be nice. They aren't necessary for a lot of rides in the mountains, but when we hit em hard, it's either a granny gear or walk!

So, will most all frames work with a triple crank? Will the chainline be ok? Does the chainstay need to be indented? Is there anything specific I should look for in a frame that I intend to build up into a triple?

thanks,
Rod Kronenberg
Fort Collins, CO