Here's a good link to making your own laundry soap. I've tried this and while mine turned out kind of lumpy, it smelled nice and the clothes seemed to be just as clean (and maybe cleaner looking because of the Oxy Clean I added).
This is the recipe I used, the linked post is a little bit different but it was so descriptive I thought it would be good to share.
1/2 bar of grated laundry soap, I used Fels Naptha which I got at Fresh Market (but I've heard it or Zote can be found at the dollar store) - edit - today I found Zote for 97 cents at the Walmart in Layton
1 cup Arm and Hammer Washing soda (I just used a couple of big scoops of Oxy Clean because I had it and love it)
1/2 cup Borax
I'm not going to type the directions because the link was so descriptive, with lots of pictures (maybe yours will turn out better than mine).
Here's that link again. Homemade Laundry Soap at The Simple Dollar
