How do I include images in the main body?

[scissorswimming]

First of all, I would like to congratulate you on all your efforts.I have been given as an essay to build the page of a class and my problems are as follows:

I don't know how to add images to the main body (meaning the part between header and footer). Which template should I visit?
Another thing is that I have been running some modules at the main body,so another question is how can I add these images to the existing modules so that they will still be on function (I mean that I would like these images mostly as a background of the modules) ?
A student has created a test page for this.Please check it out and tell me if what I'm asking is possible.

http://www.math.upatras.gr/~dany/MathSite/

Thanks in advance for all the assistance and sorry for being a pain in the neck with my silly questions

[scissorswimming]

Will anyone answer ...?
It's a amtter of utmost importance,so any help would be most appreciated.