Well sure you could use the .tgz but if you use a binary tgz anyway, you better use a rpm because thats simpler to manage, update and uninstall.
As far as i know, you extract the binary tgz files by going to the / directory and doing (as root):

# tar xfvz /home/you/gtk-gnutella-whatever.tgz

That will put the files on your system.
But as i said, if you dont use sources anyway better pick the RPM if your system supports it.

And remember to keep track if new versions get released I have the feeling that in < 2 weeks we will have another new beta