Which software is the right one for me? Newbie question

Hello there! I am a psychologist undergrad, with a great interest in mathematics. I try to implement them in my work and I'm trying to take it a little further than the usual analysis using SPSS. I am writing here because I want to use a mathematics programs for a certain job, but I don't know which one to choose. I am a complete newbiew in the subject, so I chose to post in this forum since my knowledge and time are very limited.

What I am interested in, is mathematical models that involve diagrams like for example in AMOS (SPSS), where the various boxes are related through various equations, sometimes including additional random factors. I have never used AMOS (Although I have seen others using it) and that's why I want your opinion. Can mapple or mathematica for example do this kind of job?

For those of you who didn't understand what I say let's say that I want to study how a virus spreads into a group of friends. I draw this kind of diagram

http://www.marshal.co.uk/telematics/...sociogram1.gif

And then the program assigns a random probability in each bubble ranging from 40% to 70% for this bubble to contract the virus to a bubble next to it and then it shows the result. I hope I made myself clear.

So, any suggestions?

Thanks in advance :)