From Mcabber Wiki
mcabber is in the community package repositories. Just enable it and install via pacman:
pacman -S mcabber
Mario Iseli is maintaining an official Debian package, which was successfully released with Debian Etch on 08 Apr 2007 (0.8.3). Note: After installing the package, you need to set up a personal configuration file; see the documentation and the sample mcabberrc file in the /usr/share/doc/mcabber/ directory. See the Debian mcabber package page.
Debian packages by Mario Iseli are synced to Ubuntu. See the Ubuntu mcabber package page.
Red Hat / Fedora
Michael Fleming is also maintaining packages for Fedora Core 6 (in Fedora Extras) as well as Fedora 7 and up (in the core "Everything" repository)
You only need to enable the Fedora Extras repository for Core 6 to get access - no extra configuration is needed for Fedora 7+. "yum install mcabber" installs the package and it's dependencies.
Thanks to Eric Hameleers, mcabber is now officially part of Slackware.
Thanks to Philip M. White, there is now an official Gentoo Portage.
Vsevolod Stakhov has created a FreeBSD port.
Cross compiled ipk for small NAS devices to be installed under /opt. See Optware
Mac OS X
There is a mcabber Fink package in the Fink unstable tree.
There is also a port available in the MacPorts repository.
Remember that you need to press the additional SHIFT key on Mac OS X for PageDown. That means FN-SHIFT-CursorDown for moving in the roster.