If you can copy files to the Dreambox using Hyperterminal and the 500 works the same way as a 7000 then yes.
Copy the image file to directory /tmp on the Dreambox. Then rename it using the Linux 'mv' command to root.cramfs. (at linux prompt type; cd /tmp Enter - mv imagename.img root.cramfs Enter).
Then go to dreambox and with remote select: setup - expert setup - software update - manual update - OK - and away it goes.