If you still need help, I have an article and a free hour teleseminar on this topic that you can download.
A couple thoughts:
1. PLUM will be much easier to understand if you're already familiar with binary logistic regression.
2. SPSS parameterizes the coefficients in a strange way. It actually makes it easier to interpret, but it can mess you up if you're not aware of it. I discovered it a few years ago and it took me half a day to figure out why this was happening.