After connecting to your shell account, type:
screen irssi -h the.vhost.you.want.com -c irc.servername.com
Now you can "detach" the irssi by holding CTRL and press A and then D.
You can now logout from your shell account and the irssi will stay online.
To bring the connection back online, or to resume the irssi type: screen -r
That will bring you back to the irc screen and you will be exactly were you last left off.
