Normally I used to install all the applications to a different drive other than the drive where the OS is installed. When ever I try to install an application it will automatically point to C:\program Files, where what I wanted is D:\program Files. Used to change it all the time.
Here is a small trick to change your default installation directory
1. Start => Run
2. Type regedit and press OK
3. Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion
4. Find ProgramFilesDir entry which will be normally set to C:\programfiles
5. Double click to open and change the value to the directory you want to set as default working directory.
That's all, you may have to reboot the machine.
Take care when you edit registry values.