How to make apps on Windows?

I want to make apps, but I have a PC. Is there a program I can use other than the Apple SDK to write the apps? My computer is the HP Pavilion a6238x. Any other options except buying a Mac? I'm not an adult so I don't have money for that even though I would like one. I have an old XP, could I get the Mac OS and put it in that? Well thanks