dd would work but why bother writing zero's over the entire drive if you aren't trying to hide anything?
Anyways, if you intend to use it as a dedicated file server then it might be worth it to just find the missing power cable or just buy one. Then you're going to want to look into either setting up the laptop as a SAN or a NAS type file server. I have a similar set up at my house of an old IBM Thinkpad running the FreeNAS OS
, It's a super tiny OS (can fit and boot off of a compact flash card) based on m0n0wall which is a heavily modified chopped down version of FreeBSD meant to be ran as a firewall.
For *nix systems in your network, you can mount the remote hard drive locally through SSH using SSHFS
For windows systems in your network you can map the remote file system locally using SMB/CIFS. Just go to start -> run and type "\\ipOfRemoteStorage\", enter your samba user and password (or if the remote username/password match your local one, then authentication is done automatically) then right click on the shared folder and select "Map Network Drive" and follow the prompts.
Have a good one.
"If art interprets our dreams, the computer executes them in the guise of programs!" - SICP
“If at first, the idea is not absurd, then there is no hope for it” - Albert Einstein