Here are the plans for the power rack sketched out on some graph paper. The rack didn't turn out exactly as depicted here (and I haven't added the pull up bar), but it's pretty close. Click on to see them bigger:
The whole thing is 48" x 48" square.
Again, slightly different than the final product, but you get the idea.
Also, 4" x 4" posts aren't really 4" x 4", they're 3.5" x 3.5".