The process of migrating Oscommerce to Drupal Ubercart, does involve a few processes, however, the advantages are numerous. Check out http://www.ubercart.org/drupal-ecommerce and http://groups.drupal.org/node/8096 for some data about why Ubercart/Migrating from Oscommerce. Personally I feel that the codebase of oscommerce has become very outdated and is no longer running to the potential it could. Alongside this, the Drupal project is growing and Oscommerce shrinking, with a large proportion of new modules being produced for Drupal/Ubercart.
As the first process I would recommend following this tutorial (http://www.lullabot.com/articles/drupal-data-imports-migrate-and-table-w...) to set up the Migrate, Schema and Table Wizard modules for Drupal. This can be contrasted with Dirk Gomez’s tutorial on transferral of data from Oscommerce tables to Ubercart (http://www.dirkgomez.de/en/migrating-oscommerce-shop-drupal-ubercart).