If you install it as root, I would suggest installing it to /usr/local or /opt.
For programs that you want to install in your home directory, make a program directory ~/prog and install programs to there.
Wherever you install to, make sure that you create a symbolic link to the executable into your path IE:
Code:
ln -s /usr/local/firefox/firefox /usr/bin
and then you can start firefox by typing "firefox" into an xterm
I hope this helps
--Ian