I noticed your installer uses the "Leisure Suit Larry 7.exe" rather than the "Sier.exe" -
After I installed it - I get the snazzy icon and it launches beautifully (in DOSBox, as far as I can tell; because I see the DOSBox launcher).
I did notice, however, I was playing LSL5 and exited - but stayed in DOSBox - when I CD'ed into LSL7, it told me that it couldn't run that in a Dos Window.
But Sier.exe launched in DOSBox.
So how is your icon on the desktop using the "Leisure Suit Larry 7.exe" for DOSBox?