How to make Springs end Flat?

You simply have to make an extrude at each end along your top plane to cut the spring at the dimension you want.

I prefer to build springs using sweep along a datum curve, the datum curve based on equations, and the equations driven by graphs. It makes it easy to build closed end springs. http://communities.ptc.com/docs/DOC-3063

Be aware that wound springs with fixed ends change diameter as they expand and compress. If the ends can rotate they change the number of turns; both of these are to maintain the overall wirelength of the spring.

I prefer to do springs the way David mentions above. You can then change the pitch however you like. If you are referring to grounded then ends my preferred way is to do a solidify on a datum plane that represents the flat surface of the ground. Usually you already have one datum plane where you want, then it's just a matter of creating another through the other end of the curve, offset from the first.

If you must stay with a helical sweep then just click on the pitch tab after creating your sweep profile and add points via dimensions from the start of the sweep, ratio, or via references. Depending on how you want the pitch to vary, you may have to add several points. Then change the pitch values as desired. Creo 2.0.

To make the ends Sqared and Ground, use the "Wrap" command.

Depending on exactly what you want to do, you can do as David suggested and use graphs. You can change pitch, radius, and direction (2 reverses). I did this one in 2007:

Or, you can wrap the spring easier if the diameter is constant (cylindrical). I did this one in 1999:

Or this as a wrap with closed and ground (flat as you called them) ends. There is a dead coil at each end per spec, tangent contact and nice transitions. It's also extremely robust. I did this one in 2013:

It's all great lessons in advanced geometry. Have fun!