Using command-line ftp (actual commands in bold):
ftp ftp-glast.slac.stanford.edu
use
anonymous as your login name
cd
glast.u04/rootlibs
binary (change to binary transfer mode)
get
rooclasslib_v1_linux.tar.gz (or whichever version and operating system
you are looking for)
quit
OR
Use web ftp:OR
via SLAC NFS:
/nfs/farm/g/glast/u04/rootlibs