Wow. I actually WAS the product marketing manager at an ERP company for a whopping 7 months. Worst job I ever had. Only job I was ever fired from! (This is an indictment of the specific company and management I worked for, not the job itself—-I've worked as a product manager for a manufacturing company for 9 years and do so today). Your revenue forecast needs to come, really, from your sales force. They need to tell you what they expect in new license sales, and at what confidence levels; your back end people should be able to help you with support contracts. In your business, there's a tremendous amount of year-to-year variance in new licenses (support is more predictable) because companies only buy new ERP systems once every 7 years or so.

This is not something you're going to find on the web somewhere.

Good luck.