If you're using a 64 bit version of windows then you won't be able to get DOS programs like Turbo C running. You'll need to use a virtual machine to get it going. Free options include:
- Windows 7 XP mode
- VirtualBox running FreeDOS
While I haven't tried Turbo C I've got Microsoft C 6 (not Visual C++ 6, the old DOS compiler from 1989 or so) installed on XP mode and it works fine.
Of course if you're running a 32 bit version of windows you've got another problem