Well, taking a look at the code, you can see:
xml code:
<Control xsi:type="CheckBoxControl" Id="RLnk">
<Position Top="50" Width="50" Left="4" />
<Help>Hide/Show links on logon window</Help>
<CustomLook>
<Normal>
<Unchecked>
<Element xsi:type="ImageElement" Id="Lnk01">
<Position Top="1" Left="0" Height="100" />
<Image>
<Name>normal</Name>
</Image>
</Element>
<Element xsi:type="TextElement" Id="Lnk02">
<Position Top="2" Left="11" />
<Color>
<GlobalColor>text</GlobalColor>
</Color>
<Font>
<Size>7</Size>
</Font>
<Text>Links</Text>
</Element>
</Unchecked>
<Checked>
<Element xsi:type="ImageElement" Id="Lnk03">
<Position Top="1" Left="0" />
<Image>
<Name>normal2</Name>
</Image>
</Element>
<Element xsi:type="TextElement" Id="Lnk04">
<Position Top="2" Left="11" />
<Color>
<GlobalColor>text</GlobalColor>
</Color>
<Font>
<Size>7</Size>
</Font>
<Text>Links</Text>
</Element>
</Checked>
</Normal>
</CustomLook>
</Control>
(Removed other "styles")
So, what he has done, was just using <CustomLook> to use different themes, <Normal> as theme (there were other ones), <Checked> and <Unchecked> for ticket and unticket boxes. Think now you can do it! =)
And the options window was done by skinning Messenger Plus! itself btw.