I typically install from a single DVD (same copy for years) and skip the registration process during installation. You have 30 days to activate your copy of Windows.
You will need a new key code for the PC - which you can purchase at anytime before the 30 days has expired. The DELL OEM DVD may not work - it may state that it won't "work for this type of PC" (or a similar message).
You can always give it a try...from the legal dept...."You must buy a new license for the new custom build - as the DELL OEM license applies only to the mobo/cpu of the DELL Inspiron 1440 you purchased."