The above post is a good answer...
I was able to walk, at a comfortable pace, from Mouse Gears at EPCOT FW to MGM front gate in 30 minutes. It is quite a long walk however.
The boats that run from EPCOT to MGM take a least that long. You can catch the boats just outside the International Gateway.
You can also walk to the Boardwalk or YC/BC and catch the boats there.