Esd is a sound daemon. It's used by gnome to play system sounds on certain events - like login, logout, etc.
There is one built with alsa support(the normal one) and an additional built with oss support in the AUR
There's not much to setup apart from adding esd to the DAEMONS line in /etc/rc.conf like this:
DAEMONS=(syslog-ng network netfs crond alsa esd mpd hal fam gdm cups)
-Is esd hogging your sound device and you can't uninstall it since gnome requires it to install/build?
in a startup file(like .xinitrc, or use gnome-session, kde....)
to see if anything is hogging your sound devices run fuser as root or sudo.
sudo fuser /dev/snd/*
sudo fuser /dev/sound/*
kris|~$ sudo fuser /dev/sound/* /dev/sound/mixer: 3504
Then you can use
ps auxw|grep 3504
for example, to see what is hogging the device.