I am running Mac OS X 10.5, can I still get TextSoap 6?

Yes. I'm working on making this easier down, but the steps for now are as follows:

Download TextSoap 6: http://www.unmarked.com/downloads/

Via Web store, purchase a TextSoap 7 license, adding the TextSoap 6 compatibility license option during your purchase. Use the TextSoap 6 license until you move to 10.6 or beyond, then switch to TextSoap 7 and enjoy.