How to turn off an auto Install-Shield update

Greetings all

I'm not sure if this is the correct place for this but here goes:
I have an Install-Shield Express installation which installs a number
of .EXE's and other files in a folder. Whenver I over-write these
files with a newer versions from a self-extracting zip executable, it
the launching application attempts to run one of the updated files,
Windows kicks in and re-installs the old version. This is on XP Pro
boxes, this was never a problem for Win2k. It does not seem to be a
problem on all XP boxes just some.

Anyone know of the setting to turn this off? Is this related to MSI
or Windows management console?

TIA
Jan