I'm thinking to buy an airport time capsule to make back up of my Windows PC Data. Is it possible do this?
It is possible, but having done this in the past, I would say that it would be much faster, easier, and more reliable for you to back up the PC if you connect a USB drive directly to the PC and let the Time Capsule do what is was designed to do......back up the Macs.
If you still want to try to do things the hard way, I've used two different applications in the past....to back up a PC to the Time Capsule:
Macrium Reflect.......Macrium Reflect
Genie TimeLine Pro.....Genie Timeline Professional - Genie9
Genie Timeline Pro was easily the best, but also by far the most expensive.