A. Michael Dresdner: "The odds of getting two 1/2" pieces from 5/4" stock without a top notch resaw are slim indeed. Here's the process using a table saw, but I sincerely doubt you will get full 1/2" stock from any of the boards.

"Square and surface the boards S4S with the two edges at 90 degrees and straight. Set your blade as high as it will go, and set the fence so that the blade splits the wood in the center. It will cut just over a third of the way through. Flip the board and cut the other edge with the same face against the fence. You will now have an H shaped board with a small web in the center. Assuming you do not have a band saw, you can cut this web with a hand saw. The table saw cuts will act as a guide. Once split, remove the web remains with a hand plane or planer."

A. Simon Watts: " You don't have much margin for re-sawing so I suggest investing in a thin-kerf rip blade. Set the fence to bisect the board, raise the blade about halfway and make your cuts. Then raise the blade and cut again. If the two cuts don't quite meet finish the job with a handsaw."