here is a 4 month reply
first of all if you were to of done this properly, you should of RAID the two harddrives
but since you did not (and you can no longer do so, without reinstalling the OS)

# ssh root@server.com
# fdisk -l
find your second harddrive in the list, should be something like /dev/sdb or some shit
#mount /dev/sdb /somewhere/you/want

you cannot add it to your home directory, if it's not empty
you can add it to a user subdirectory, or a new user
the key point, is that the directory has to be empty

the most use for this harddrive i recommend is putting it as a backup drive
mount it to /home/backups
and thow all your backups to it

if you want apache to write to it, or however lxadmin works
you must add the software user id and give them at least group access to the drive