can't install apps in apps folder


I was installing LimeWire on my Mac on Mac OS X 10.0.3 but it doesn't work!

When I change to /Applications as the installation directory the LimeWire installer chokes and says that i do not have enough system credidentials. Then I enabled root and tried again. It didn't work.

In fact, Computer (from the Go menu in the Finder) has a little pencil with a cross, which I guess means that the HD is write-protected. But why? How do I ever get LimeWire into the Applications folder?
Are you logged in with the administrator account? If not, it won't let you write to the Applications directory. Also, if you want to make sure that the directory's permissions are set properly, open the Terminal and type these commands:

su root [i](Enter your root password)[/i]
chown root /Applications
chgrp admin /Applications
chmod 775 /Applications

If all goes well, it will set Applications to be writeable by root, or the administrator accounts, but not by everyone else.