I'd agree, osCommerce is a fantastic piece of kit! Designed
THIS SITE around the osCommerce engine earlier this year for my girlfriend (the things you do for love, eh
??). Once you get the hang of how it works (which can take a while) it's fairly easy to customise.
Some of the mods I'd look out for are:
And if you know a bit of PHP, adding your own features to it shouldn't be too hard either. I build an automated email reminder service that sends emails to customers to remind them of events they choose, complete with links to products on the sites. It doesn't really adhere to the osCommerce way of coding (functions etc) but I'm just getting to grips with PHP, so just to get it working was enough for me!!
All the best with it, and like the others say, make good use of the osCommerce forums out there: I found them a God-send at times!!
Phil