I use Xfce4. Zenity is available -- and when I let it open a test window (--warning), it shows up in my regular Gtk theme. I do not have kdalog installed. Winetricks still uses xmessage instead of Zenity. I saw in the script that you're doing a check for what desktop environment is running, it's probably a good idea to just check for the existence of Zenity or kdialog after that so it'll use either of those anyway.
