Added modules for using Nivo Slider in Header, Footer, Front Page and Index.
If you want to use it with the last two options, you need to install the correspondant addon
Modular Front Page: http://addons.oscommerce.com/info/7626
Modular Index: http://addons.oscommerce.com/info/9363
No credits at all for me. Everything done with the unvaluable help of f.figue (thanks, dude)
To be done: He also says that it would be great to make different styles for each module, and create a module for header_tags, since up to now .js and .css are called for each module installed.
Anyway, now is fully functional, while further development is awaiting.