Backup Server

We are using Window NT 4.0 PDS and at present there is no Backup Server (BDS) support. In the primary server lot of Sofware has been installed along with them one of the S/W Retail Pro has been running with Hardware Lock. Presently the HDD is almost full. If we go and setup Backup Server with a higher configuration and higher capcity HDD for the present PDS and promote the BDS to PDS will solve my problem? Another question is the Retail Pro in the BDS m/c promoted to PDS will work smoothly or not if I am changing the Hardware Lock to the new machine?