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: http://aur.archlinux.org/packages.php?do_Details=1&ID=6703&O=0&L=0&C=0&K=esd&SB=&SO=&PP=25&do_MyPackages=0&do_Orphans=0&SeB=nd
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.