I got the duplex mode to work. There was another ppd file that I had on my SuSE system so I just copied that one over to Puppy also. I don't remember where I got the original from, maybe from the Samsung install disk. So, the 2 ppd's are named:
samsungCLP510.ppd and CLP-510splc.ppd.
I tried it out in AbiWord but the duplex mode still did not work. Then I tried it out in another word processor, Leafpad, and that one worked beautifully!