Can I create a box or gui around a conversation options?
Yes, you can assign a "window" object to the response box.
And can I add some Icons next to the options like in MI?
No, currently the options can be either a simple text (that's what you can see in the WME demo) OR icons (Broken Sword style).
Also, is there anyway I can make a LEC GUI like COMI and MI 1 and 2?
COMI - yes; MI 1 and 2 - yes, but you'd have to design the scenes with respect to the verbs/inventory area.
Is there a way of adding a text parser to the GUI?
Well I think it would be possible to write some simple parser, but it would require a lot of scripting...
Can we add menu's to the GUI like in the early Sierra games?
You could build a menu system using the WME's windows and buttons, but it probably wouldn't behave exactly the same like the Sierra style menus.
Basically, what kind of stuff can it do? Its a little difficult to understand fully what its capabilities are.
Yes, the GUI layer isn't yet documented, but basically you can create "windows", those can have a backround image, title bar etc., plus the windows can contain other windows and "widgets", such as buttons, single line editors and static texts or images. Using these simple elements you can build up rather complex interfaces.
In the future plan to add more widget types, like sliders and some simple HTML viewer (something like the Sidney computer in GK3 or the PDA in Spycraft).
And will you ever be able to compile the game into a single EXE?
No, it will always be the EXE plus one or more package files (*.dcp). You can build the packages in ProjectMan using the "Compile packages..." command.