osCommerce question

Due to circumstances beyond my control I have to set up a second storefront on one of my domains and the recommended package was osCommerce. I have downloaded it and, with precious little help from the scanty included documentation and the confusing online knowledge base, successfully got it set up. Unfortunately, I then found out that what I had successfully set up was the demo store and none of the included modules gave any indication as to how to convert it to a working store. I have since found that it is composed almost entirely of interlinked php files that have to be modified very carefully or the files will be ignored by the files linked to them.

Is there anyone here who has set up a storefront using this package that would be willing to give a relative newbie to PHP some advice on how to make changes to this thing without causing damage?