Not sure what you mean by picking up the new computer.  The agent is what ties the computer to the DS Server.  Where I work, a login script installs the agent if it isnt already installed.  This will allow the computer to register itself with the DS server.  If you are adding a new system, I usually add the MAC address.  This way when you try to image it the system knows that paricular machine has a job waiting for it (might be able to use the serial number but we dont do that here so not sure if it would work).

I am also going to be using a login script to install the agent. I was speaking of a brand new computer(s) and was figuring the MAC address is what it needed. I usually don't get that anyways. thanks

We're also using MAC addresses.

You might speak with your hardware vendor or reseller.  After asking ours included the MAC address along with the serial number and our PO information on the packing slips.  Eventually we got them to e-mail this information to us ahead of time in an excel spreadsheet.  It made it really easy to import that information afterwards.

Just make sure to leverage those Value Added Resellers (VARs).  Don't be afraid to make 'em work to add value.