Whilst not wanting to import the full oscommerce I have been looking at getting some kind of shopping cart there.
At the moment I have too many other addons on the go.
The main think when looking to integrate a package is to see if its easy to import into the Smarty template layout which Tiki adopts. If oscommerce is just an engine I would have thought it would be quite easy.
Whats the license? Remember tiki is LGPL