RE: S-curve exported to excel
In order to get the curve properly, there are few requirements such as properly statused schedule, coasted resources assigned to tasks and a baseline and ofcourse complete tasks. As far as I know about MS Project, it will not give you data to the right of the status date if you want to generate data past the status date. So make sure you are setting the status date past the last day of your project. Once done, try exporting the data to MS Excel and see if you get any problem in getting curve.
re: How to build an S curve with the help of project
you posted the question surely you already know how to construct an S curve with the help of project :) but I needed to do and did not know and did not find anyone teaching. I took a poke around in the reports of the project and found out, then I'll post aki to help others.