Rather odd - coulnd't fnd any specs on the Athlon TK series. In any case, the power rating will make a difference in heat, battery life and weight of the laptop. Just keep in mind that the processor isn't the only factor. For the same dollars, what are you getting in terms of memory, video, burners, wireless capability, and other perephrials?
Although I can not find one today, they keep popping up at places like TigerDirect.com, Newegg.com, and even Zipzoomfly.com. Your other choice is to go with an Opteron 180, which seems to be the Opteron version of the 4400+. If your system supports it, you could also go to the Opteron 185 which is equivalent to the 4800+. 939s are no longer being made, so make your decision soon.