Laminate wood floors are designed to ``float'' on a foam underlayment, snapped together like puzzle pieces. They're not attached to the surface by glue or nails, but just held in by the floor trim. This makes them remarkably easy for the do-it-yourselfer to install, as compared to traditional hardwood planks. However, if the room is out of square, as old rooms often are, you'll have the same problems getting the planks to line up with the walls and not look crooked. One solution is to lay the flooring diagonally.
Use your hammer and prybar to carefully remove all the floor trim in the room. Don't break it, as you'll need to re-use it. Remove the nails and set the trim aside.
Roll your foam underlayment out along the longest wall in the room, cutting it at the end with your razor knife. Lay the next course of underlayment alongside the first, taping them together with a long strip of flooring tape. Continue until you've covered the whole floor.
Measure and mark the middle of each wall at the floor. Use your chalk snapline to lay two intersecting lines across the floor from those marks. Use your square to ensure that the two lines are at exactly 90 degrees to each other where they intersect, adjusting the line as necessary. (If your walls are crooked, then just using the mid-wall measurement will give you a crooked line).
Measure four feet out along the lines in all four directions from the intersection, and mark them. Use your chalk snapline to connect each of the marks, so you have large a diamond shape encompassing the intersection. Measure each side of the diamond, find the exact middle, and mark it.
Decide which two corners of the room you want the diagonal floorboards to point toward. Lay your chalk snapline in that direction, so that the line crosses the middle of the intersection. Make the line also cross the centre marks on the two sides of your diamond shape that run perpendicular to the direction you want your flooring to go. Snap the line, so you have a diagonal line running all the way across the floor.
Lay your first course of laminate flooring along one side of your diagonal line, setting them unattached on the foam underlayment. Snap the boards together end to end. Use your mitre saw to cut the final pieces on either end at a 45-degree angle, leaving 1/4 inch of space from the end of the board to the wall to allow for expansion.
Lay your next courses of floorboards in the same manner, snapping the tongue-and-groove connections along the sides and cutting your end pieces at 45 degrees as necessary. Remember to leave a roughly 1/4-inch gap at the wall from each cut. Continue until you've laid the whole floor.
Re-install your trim using a trim nailer. The trim should sit directly on the flooring, holding it down and covering your 1/4-inch gap. Make sure when you nail in the trim that you're nailing through the wall and not into the floor.
Wear protective eye goggles when using your mitre saw.