There are some solutions to transfer store data from osCommerce to Magento.
- W2: Follow migration guide to migrate data manually from old cart to Magento.
- Back up your database
- Copy all your osCommerce product images into media/import
- Change the language for the admin interface to English (United States) - or no products will appear even after a succesful import. You can switch it back afterwards
- Set up your import profile (from System > Import/Export > osCommerce)
- Click on Run Profile on the left, and then the "Check Requirements" button
- If you only have one store/website, the Website Code field will be "base"