wrestool isn't POL's dependency so it won't work for everyone, but you can use icon from ~/.local/share/icons. You can see how it's done here
You can also use cover of the game from wikipedia. How to do it is also in the same script.
Ok, here is the updated version:
#!/bin/bash
# Date : (2010-05-23)
# Last revision : (2010-05-23)
# Wine version used : 1.1.38
# Distribution used to test : Ubuntu 9.10
# Author : Marco Gerards
# Licence : GPLv3
# Depend : none
[ "$PLAYONLINUX" = "" ] && exit 0
source "$PLAYONLINUX/lib/sources"
TITLE="Jerusalem: The 3 Roads To The Holy Land"
AUTHOR="Marco Gerards"
PREFIX="Jerusalem"
PREFIXDIR="$REPERTOIRE/wineprefix/$PREFIX"
WORKINGWINEVERSION="1.1.38"
POL_SetupWindow_make_icon_for_shortcut()
{
convert "$HOME/.local/share/icons/$2" -geometry 32X32 "$REPERTOIRE/icones/32/$1"
}
wget http://upload.wikimedia.org/wikipedia/en/0/06/Jerusalem-_The_Three_Roads_to_the_Holy_Land.jpg --output-document="$REPERTOIRE/tmp/leftnotscaled.png"
convert "$REPERTOIRE/tmp/leftnotscaled.png" -scale 150x356\\! "$REPERTOIRE/tmp/left.jpeg"
POL_SetupWindow_Init "" "$REPERTOIRE/tmp/left.jpeg"
POL_SetupWindow_presentation "$TITLE" "Cryo" "http://www.cryo.fr" "$AUTHOR" "$PREFIX"
select_prefix "$PREFIXDIR"
# Let the user select a CDROM
POL_SetupWindow_cdrom
# Check if this CDROM is the correct CDROM
POL_SetupWindow_check_cdrom "/Jerusalem.msi"
# To make sure the user has the same environment as the game was
# tested with.
POL_SetupWindow_install_wine "$WORKINGWINEVERSION"
Use_WineVersion "$WORKINGWINEVERSION"
POL_SetupWindow_prefixcreate
Set_OS "win98"
PROGRAMFILES="Program Files"
POL_LoadVar_PROGRAMFILES
# Run the installer
POL_SetupWindow_wait_next_signal "Installing game..." "$TITLE"
wine msiexec /i "$CDROM/Jerusalem.msi" /q INSTALLDIR="C:\\\\$PROGRAMFILES\\\\Jerusalem"
POL_SetupWindow_detect_exit
wine reboot
# Make a short cut
POL_SetupWindow_make_icon_for_shortcut "$TITLE" "*_jerusalem.0.png"
POL_SetupWindow_make_shortcut "$PREFIX" "$PROGRAMFILES/Jerusalem" "Jerusalem.exe" "" "$TITLE"
Set_WineVersion_Assign "$WORKINGWINEVERSION" "$TITLE"
# Done!
POL_SetupWindow_message "$TITLE installed."
POL_SetupWindow_Close
exit