Thank you for reply.
The only way to transfer your data from osCommerce to VirtueMart Store Manager is to use import/export tool. You need to export all your data from osCommerce to .csv file and then import this file into Store Manager for VirtueMart. Not all fields may be transferred due to differences in database fields of these shopping carts. You are welcome to check this documentation to see how import process goes like:
http://store-manager-for-virtuemart-documentation.emagicone.com/products-management/import-products
Please, let me know if any additional questions occur!