For one, don't use 1.1o. It is flawed (and has some pretty scary bugs). Get 1.1z from
The problem with write not working in win98SE is that on win9x write.exe is in $WINDIR, and in winnt it is in sysdir. There are two ways of dealing with this:
Option 1: check for existence of each:
IfFileExists "$SYSDIR\write.exe" 0 2
Exec '"$SYSDIR\write.exe" "$INSTDIR\Readme.doc"'
Jump 1 ; don't execute twice
Exec '"$WINDIR\write.exe" "$INSTDIR\Readme.doc"'
Option 2: use ExecShell:
ExecShell open '"$INSTDIR\Readme.doc"'