To launch your new Gnome build, you need to add or modify some files. The instructions vary depending on whether you use a graphical login screen, or a text login screen. Although not necessary, it is often helpful to copy themes and icons from your old Gnome installation to your new one (especially if you have installed extra ones from art.gnome.org). Also, if you are not creating a new user to log in to the new version of Gnome with, you may want to consider moving potentially conflicting dot files out of the way.
In order to launch your new version of Gnome from your graphical login screen, you have to add some files. The graphical login screen program varies from distro to distro (some use KDM or XDM), but these instructions will concentrate on GDM. You first need to create /etc/X11/gdm/Sessions/GNOME-CVS with the following lines:
#!/bin/sh exec jhbuild run gnome-session
Then make sure to run chmod a+x /etc/X11/gdm/Sessions/GNOME-CVS to make that file executable.
The newer versions of GDM (either that or the modified versions that Fedora ships) uses a different format. In this case, you also need to create a gnome-cvs.desktop file under /etc/X11/dm/Sessions/ with the following lines:
[Desktop Entry] Encoding=UTF-8 Name=GNOME-CVS Comment=This session logs you into GNOME-CVS Exec=/etc/X11/gdm/Sessions/GNOME-CVS # no icon yet, only the top three are currently used Icon= Type=Application
Make sure to also make this .desktop file executable by running chmod a+x /etc/X11/dm/Sessions/gnome-cvs.desktop.
In order to launch your new version of Gnome from a text based login, you need to modify your ~/.xinitrc to contain the line
exec jhbuild run gnome-session
Note that older themes may not work with your new cvs gnome installation. For example, trying to copy the Red Hat 8.0 icons to my new Gnome 2.3 installation didn't work. Copying them from Red Hat 9 did work. The icons weren't any different, but apparently their names and locations on disk were. You may run into other changes. The following has usually worked for me, however.
Also, these files and directories may or may not exist on your system (e.g. Bluecurve directories tend to only be found on RedHat systems, H2O-gtk2-* directories were from themes I donwloaded off art.gnome.org, I created the backgrounds directory on my old installation from pictures I downloaded from multiple places, etc.) However, they should give you an idea of the locations to look and where to copy files to.
Copy Bluecurve gtk2 and metacity themes
cp -a /usr/share/themes/Bluecurve/ /opt/gnome2/share/themes/
Copy the H2O-gtk2-* gtk2 themes
cp -a /usr/share/themes/H2O-gtk2-* /opt/gnome2/share/themes/
Copy the Bluecurve icons, which are unfortunately in multiple places (I may have missed some, too)
cp -a /usr/share/icons/Bluecurve /opt/gnome2/share/icons/
cp -a /usr/share/pixmaps/nautilus/Bluecurve/ /opt/gnome2/share/pixmaps/nautilus/
cp -a /usr/share/pixmaps/redhat* /opt/gnome2/share/pixmaps/
Copy some background images to a directory I'll be able to find (I like having lots of background images in one directory, rather than having them all over the hard disk, even if that's allowed).
cp -a /usr/share/backgrounds/images/cool/ /opt/gnome2/share/backgrounds
It is possible that your dotfiles will conflict with the gnome you just built from cvs. It happened to me once (during the Gnome-2.3 development cycle), though it has not happened since. If you want to use your cvs installation with a current user account and want to be more cautious than me, it may be useful to do the following before you launch your new version of Gnome. I just moved all dotfiles that I thought could possibly be relevant to a backup directory. It is probably best to do this when logged out of gnome. (I just log out and then use Ctrl-Alt-F1 to go to a virtual terminal and do the dirty work from there, returning to the graphical environment with Ctrl-Alt-F7). Here are the commands I used:
cd ~/ mkdir backup-dot-files mv .gnome* .gconf* .nautilus Desktop backup-dot-files/