what do you have in /usr/src directory?
when i was installing gnome last time, i had only kernel sources and had no problems....
anyway, if you going to install any/all sources, i would use sysinstall and then modified cvsup to update them (if you want to)
This is my supfile, i was using to update my sources just 3 days ago
Code:
*default host=cvsup3.lv.freebsd.org
*default tag=RELENG_7_0
*default prefix=/usr
*default base=/var/db
*default release=cvs delete use-rel-suffix compress
src-all
bold lines are the ones you might want to edit
http://www.freebsd.org/doc/en/books/handbook/cvsup.html
P.S.
and why i don't want to just fetch sources with csup????
A: it's dam slow