If you are doing a clean install...and you get 7B STOP errors during an attempted install...I would say that you need to delete the existing install.
If you are trying to do a repair install, the 7B indicates a problem with your existing system (I think).
Since you have an HP system, you may be trying to install from recovery/restore CDs. All I can say about such is that you need to read up on how these disks are expected by the manufacturer...to be used.
Info on 7B errors at http://www.aumha.org/a/stop.htm
, 7B on the left. See if any of the situations listed under 7B meet yours.