By default Windows installs all programs into the C:\Program Files and C:\Program Files (x86) directories. If the hard drive you have the operating system installed on is running out of space though, or you just want to have the OS on a separate SSD, you might want to consider changing these default installation paths.
Be warned before you go on though! Microsoft does not officially support changing installation directories (see here). You are responsible for all consequences.
Furthermore, since we are going to edit the Windows registry for our causes, you should have that backed up first in case something goes wrong. Here's how: http://www.faqforge.com/windows/backup-your-windows-registry/
Now that you have been warned, let's get started: Open a Run... prompt and enter regedit. I will be referring to our new installation path as E:\Program Files and E:\Program Files (x86), so replace these paths with the ones you want to have (you can choose other names as well). Now browse the left registry pane for the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion key. Click on that key once to show its contents and locate the ProgramFilesDir and ProgramFilesDir (x86):
Double click those values and change C:\Program Files to E:\Program Files as well as C:\Program Files (x86) to E:\Program Files (x86). Furthermore it might be safe to change all other paths directing to the old directories to point at the new ones as well. That's it if you are on a 32bit system, close the registry and reboot your computer.
64bit users have one more step to go. Close the registry and open another Run... prompt. This time, enter %systemroot%\sysWOW64\regedit. Another registry windows will open. Repeat the exact same steps here that you have done before. Afterwards, close the registry and reboot your computer.
