We're going to start collecting and publishing all the little mods and hacks and tricks we've put into our zen cart installation. Zen cart is an open source shopping cart, its very powerful and we really like it! One of the beauties of open source is how easy it is for us to customize and tweak out the system, which lets us do what $10,000 shopping systems can't do!
These mods are for 1.3x versions of zencart and are probably adaptable to OScommerce. They are all released public domain (or whatever license the original file had if it's a direct mod of existing code).
These codes and mods are TOTALLY UNSUPPORTED, are not guarateed for anything and may not be fit for any use! They may not work, they may break your store, they may cause you to lose money, they may set your cat on fire. Do not use them unless you are good with LAMP systems (and if you aren't sure what LAMP stands for, its likely you are not).