Here a little script you can use to generate user accounts if you're running with AuthMode=Registered:

#!/bin/bash

BITLBEE_BIN=/usr/sbin/bitlbee

echo -n 'Username: '
read user
echo -n 'Password: '
read -s pwd; echo
echo -n 'Repeat password: '
read -s pwd2; echo

if [ "$pwd" != "$pwd2" ]; then
        echo "Passwords don't match." >&2
        exit 1
fi

hash=$($BITLBEE_BIN -x hash "$pwd")

echo "<user nick='$user' password='$hash' version='1'/>"