Of course they are! You can find it in the INTERFACE-1 resource. I don't know how MessengerPlus!'s skinning engine works, but you can change the resources using a normal resource editor like resourcehacker (google it).
Here's is the XML tag which describes the floating contacts window:
code:
<Window Id="FloatingNickname" Version="1">
<Attributes>
<Caption>Floating Desktop Contact Nickname</Caption>
</Attributes>
<TitleBar>
<AllowMinimize>false</AllowMinimize>
<Title>
<Prefix>Full</Prefix>
<Text/>
</Title>
</TitleBar>
<Position Width="225" Height="103" InitialPos="Normal"/>
<DialogTmpl>
<BottomBar Style="None">
<RightControls>
<Control xsi:type="ButtonControl" Id="BtnOk">
<Position Top="0" Width="50" Left="0"/>
<Attributes>
<IsDefault>true</IsDefault>
</Attributes>
<Caption>&OK</Caption>
</Control>
<Control xsi:type="ButtonControl" Id="BtnCancel">
<Position Top="0" Width="50" Left="0"/>
<Caption>&Cancel</Caption>
</Control>
</RightControls>
</BottomBar>
</DialogTmpl>
<Elements>
<Element xsi:type="ImageElement" Id="ImgTitle">
<Position Top="8" Left="7"/>
<Image>
<Name>buddy-floatingnickname</Name>
</Image>
</Element>
</Elements>
<Controls>
<Control xsi:type="StaticControl" Id="LblTop">
<Position Top="8" Width="175" Left="29" Height="20"/>
<Transparency>160</Transparency>
<Caption>You can set a special nickname for this contact that will only be used in the floating desktop window.</Caption>
</Control>
<Control xsi:type="StaticControl" Id="LblNickname">
<Position Top="35" Width="72" Left="7"/>
<Attributes>
<AutoAdjustWidth>true</AutoAdjustWidth>
</Attributes>
<Caption>Contact's nickname/Caption>
</Control>
<Control xsi:type="EditControl" Id="EdtNickname">
<Position Top="33" Width="127" Left="81">
<TranslationAdjust>
<StaticCtrlIDLeft>LblNickname</StaticCtrlIDLeft>
</TranslationAdjust>
</Position>
</Control>
</Controls>
</Window>
You can modify the values in order to remove paddings, and make it more compact.
Hope that's it !