I would start by going to salesforce.com and contacting their sales department and try to get them to direct you to someone who might get you started in the right direction. They can most likely supply some of their own testing process, or at least give you an outline of their testing methods. I'm sure your company is not the first to utilize them. Gather as much information on the testing process and maybe even contact one of the other companies integrating with salesforce. Then when you have gotten enough data, start thinking about how you would go about testing it. Actually I imagine you will be concentrating on the interface between your product and salesforce so protocols will be something to look at initially.
Success is the ability to go from one failure to another with no loss of enthusiasm.
~ Winston Churchill ~