I think you misunderstood me, What i'm trying to do is run marsinst.exe from CD, no problem, but i need to run an installer which must be ran from the root of the installation drive, Which will be, more than likely, C: drive or whichever drive/partition the OS is installeed to. Example: In RunOnceEx i would have used: "%SystemDrive%\installer.exe" Obvioulsly that does'nt work in marsinst.ini as it does'nt reconise it as a valid varible. So therefore: Run1="%SystemDrive%\installer.exe" Will not work. Your help is appreciated, Thank you