the reason it doesnt work on worm net is because when you connect they send a packet to your pc, the exe then tries to read a specific sector (sent via the server in the packet.. thus totally changeable easily), crc's it and then sends the crc back to the server for 'validation'...
initially it was sector 0x17171717 (team 17 - cute eh), invalid sector, next day they started using 'correct' sectors (within the sector range of the cd)..
which explains why a no-cd exe wont work for worm net
full image mounted should work though..