[kh99]

What you really should do is have a test site in debug mode, by putting $config['Misc']['debug'] = 1; in include/config.php. Then you can go to Products & Plugins -> Manage Products in the adminCP, and "edit" the product. You'll then have text areas to put in install and uninstall code. When you've got the product the way you want it, you can export it to an xml file.

If you really want to do it by editing the product xml file, probably the best thing would be to find an existing product and see where to put xml tags for installcode and uninstallcode. It's a little complicated by the fact that you can have different sections of code for different versions, to support updating.