I install windows 7 in fedora running system without overwrite the previous OS.but the problem is if i install windows 7, it shows 2 os's when starting my system.I want to boot my system in fedora by default.what's the solution??????????????

So what is wrong with the grub ?? and I didn't get what you want exactly , what did you mean by

I install windows 7 in fedora running system
??
windows 7 isn't applicatuin to be installed in fedora

To run it in a running Fedora system, you need a virtual machine manager such as VMware or VirtualBox so you can install/run Windows in a virtual machine. That way, your Fedora applications continue to run while you simultaneously run Windows applications. I do that all the time.

if you want dual boot system
  1. install windows 7 in first partition or /dev/sda1
  2. then istall distro linux your like
  3. grub will auto detect your windows
use virtual box or qemu

$ qemu -cdrom YOUR_DISTRO.iso -boot d -m 1024

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