ERP = Enterprise Resource Planning which is a term that seems to have been created to encompass the entire process. There are several ERP softwares out there, including stuff from SAP, JD Edwards, Peoplesoft and now Microsoft. It’s an attempt to manage the entire Enterprise, from planning through procurement, manufacturing and then outbound logistics and warehousing.
As to Supply Chain Management, this term will mean slightly different things to different companies, depending on what they define as their Supply Chain and how the internal turf is divided. It should really include forecast and at least some of the manufacturing processes as well as the “outgoing” stuff mentioned before. The idea is that you have everything you need, when you need it, so that your Supply is equal to (forecasted or actual) Demand.
What ERP adds to that is mainly Accounting and Financials, possibly some forecasting, depending on the previous definitions. Quality and Maintenance might be others that are usually not thought of as pure supply chain but are equally important. In complex systems HR can even be mixed into the bag, so that you know that you have enough staff (and that they are adequately trained), optimizing them like any other component in your production process.
Oliver Wight would be one group that consults with major manufacturers and helps them define their Supply Chain and how best to manage it (defines what are their current best practices). I’m sure that there are others out there like that.