These OS's are no longer supported so the REAL solution is to upgrade. This happened to me. You can install Sage on a WIN 7 WS, then copy the folder to the 2003 Server. This should suffice until you have to install any product updates at which point you will have to copy the folder back to the WIN 7 WS, install the PU, then copy back to the 2003.
Not possible to install the workstation client to the XP. There may be some workarounds, but you will be money ahead in the long run to just upgrade your machines and the OS. As I said, OS is no longer supported and the machines have got to be dog slow in processing.