Whenever you install new program on your windows XP machine it is installed in C:/Program Files directory as the default directory.But if you want your program to be installed in different directory other than C:\ Program files and you dont want to change directory each time you install a program to that particular directory then you can change the default installation directory by applying some tweak to your registry
GO to "Run"
type "regedit" press enter
Then go to
"HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Windows/CurrentVersion"
Go to the entry named ProgramFilesDir and change its value from C:/Program Files. to desired location.
Now the new location will be used as the default installation directory for new programs.