A bit more development from here and it'll lead to 2.8.0 stable.
How to get and run 2.7.90 (on Linux or *BSD etc):
1) Figure out how to install programs on your system. e.g:
Fedora: yum install <program>
Debian/Ubuntu: apt-get install <program>
2) Install all of these: gtk2-dev[el] autoconf automake m4 cvs gcc gettext
3) Get the xchat source:
cvs -d:pserver:anonymous@xchat.cvs.sourceforge.net:/cvsroot/xchat login
(no password, just press enter)
cvs -z3 -d:pserver:anonymous@xchat.cvs.sourceforge.net:/cvsroot/xchat co -P xchat2
4) Compile it:
cd xchat2
./autogen.sh
./configure --enable-maintainer-mode --prefix=/usr
make
make install (as root)
5) run xchat!

