First give the owner ship of the mount point,
# chown [users]
# chmod 775
add a line in /etc/fstab and in /etc/mtab to make it auto mount,
with fstab, it'll auto mount any disk stated in /etc/fstab file, withmtab,
it'll mount the disk is inserted.
/dev/sda1 /media/usbdisk ext3 rw, (state the options you want).
here make sure, your mount point is /media/usbdisk or what ever the nameyou
In Gnome, mount/unmounting of removable media is automatic provided it
is allowed in the hal configs. Check entries in the hal configs.
Secondly, you should prevent the filesystem check being applied to
this file-system at boot time by putting a 0 in the fsck column.