I redirect you to these three posts. Use any graphics program capable of producing a paletted bitmap file, and turn it into a blocks file using J1E, JJ1MOD, Jazz Graphics Pack, or good old bmp2blox if you can find it. (Really, though, just use J1E.)

As for behaviors, I'm pretty sure the shareware includes behaviors used in later levels, it's just harder to know what they do since all you have to work from is DD's brief notes. But that's a minor point.