The exe i run is called PCX_PC_Extender_11.1.058,01_Prod.exe
I have since re-installed the 755 with a Dell supplied OEM copy of XP with SP3. This has allowed the PC Extender to install.
Wyse support have provided a dev version via FTP for me to test and also asked me to check the SATA operation modes on the boxes.
Will update this thread when I know more.