Adding a feature to OSCommerce

I need to add a new feature to OSCommerce. I have a MSSQL base ERP. Every customer (resellers) has an ERP - CUSTOMER - ID e a CUSTOMER - ID in OSCommerce. And now i want to add a new feature to it. It's necessary to create a function to read the current turnover ( amount of $ ) from this MSSQL database ( by ODBC ), and show-up this the reseller when he logs on OSC-site. A field will be added to the OSC customer table, storing the ERP correspondent Customer-ID.