I checked out both links posted. They are both for an "envelope type" bag. They will work, however, if you include the dimension of the bottom in the height measurement. I would probably do that if the bottom isn't very wide.
You can make a lining for a "box type" bag. I made a http://www.blacksheepbags.com/booga_bag.html
, which has a very definite "box" shape. I sew, so I figured this out and decided to put a pocket on the inside as well. I took a piece of fabric and cut it as a rectangle to match the sides of the purse (top to bottom, wrapping around all four sides). Add seam allowances. Also, I cut a rectangle the size of the bottom and added a seam allowance there. I sewed the bottom to the sides, and then did the seam up the sides last. Don't worry if it's not great, it's on the inside of the purse.
Hope that helps.