Good news!
We all know that the
q3map2 compiler got support for Tremulous added in the RC1 release (about it:
http://tremulous.net/phpBB2/viewtopic.php?t=2774 and
http://tremulous.net/phpBB2/viewtopic.php?t=3298). Today, to complete the support for the best open-source game,
GtkRadiant team added to their packages the files needed to edit Tremulous maps! Now you can choose "Tremulous Support" from the installation program:

This will install the file
trem.game in C:\Program Files\GtkRadiant 1.5.0\games and will create the folder C:\Program Files\GtkRadiant 1.5.0\
trem.game that contains two folders:
base and
docs. The Docs folder contains some old but useful manuals from Quake3. The Base folder contains the
entity list and the
default shader list.
To really feel the full power of the Tremulous support, you will need to
copy or move the following files from that Gtk Base folder to your Tremulous Base folder (C:\Program Files\Tremulous\base):
common-spog.pk3,
common-mgturret.pk3 and
common-strands.pk3; also move the folder
Scripts (C:\Program Files\GtkRadiant 1.5.0\trem.game\base\scripts) to the Tremulous Base folder.
The first pre-release version with the Tremulous Support was that: GtkRadiant-1.5.0-2007-03-04-OVERLORD.msi
(You can browse the folder
http://zerowing.idsoftware.com/files/radiant/nightly/1.5/ for previous and newer releases)
Current version (1.5 Final):http://zerowing.idsoftware.com/files/radiant/GtkRadiant-1.5.0.msi