Have a read at this before you do anything, it's the Dbox2 Bible.
Digital Kaos - Downloads - PT-1s Dbox2 Helpfile
Before you flash another image, connect the box to your PC and connect to it using an ftp program. Take a copy of the /var/keys folder and save to your PC.
You have two methods to flash.
1) Using IFA
This is a bit of software that connects to the box and flashes the image.
Guide - Digital Kaos - Downloads - IFA Guide
Tool - Digital Kaos - Downloads - Image flash assistant v1.56
2) Using FTP and onscreen menus
You need the box connected to your PC via a crossover ethernet cable. You use an FTP program to transfer the .img to the /tmp folder on the dbox2. Use the remote and onscreen menus to flash it.
Write One Partition
Flash Without Bootloader
Choose img file from the list and press OK. It will take approx. 2 mins to flash and then reboot. DO NOT interrupt the flashing process or power off the box.
There are loads of begineers guides in the download section.
Digital Kaos - Downloads - Guides
And any of the images in the download section will sort you out. Then you need to know how to add keys and roms but we'll come to that once you flash it.