I have made some progress. After enabling the RPCSS DCOMLaunch plugin and altering the DCOMLaunch.INF I have a 2003SP1 BartPE that now allows me to start DISKPART, list disk information, clean disks, create an extended partition etc. but when I attempt to create a primary partition I get the "disk management serice cannot complete..." error again. Currently I am only working on a VMWare 5 machine so may try some physical hardware and also a vanilla WinPE 1.6 image instead of BartPE. Still it is strange that the older BartPE built from Win2003 (no SP) is still working fine.