All in all, the total tree size for the XEmacs core tree is 196MB, comprising over 2006 files with 397754-some odd lines of code. Packages add another 4042 files for 760315 lines of lisp. You only need to do this once, as it will create a file in your home directory called .cvspass with the necessary data. Now go the the place you want to put the tree, and actually check out the current version. One xemacs-21.5 directory complete with the latest versions of the base code.
Packages are separate, of course.
The -d option says what to name the new CVS directory tree. The -z3 option enables compression during transit, and speeds things along tremendously. The -r option specifies the CVS branch to use. There have also been reports that some files are not created unless -Pd is used with cvs update . XEmacs developers do CVS commits on an irregular basis.