already there, mate. there is an info tag you can use -- network.ipaddress. but you need to add it to home.xml on your own.
you can even use the visible tag of system.hasnetwork to hide it the tag if there's no network connection.
here's a start for you:
<control>
<description>ip address label</description>
<type>label</type>
<id>0</id>
<posx>###</posx>
<posy>###</posy>
<width>###</width>
<info>network.ipaddress</network>
<align>right|left|center</align>
<font>somefont</font>
<visible>system.hasnetwork</visible>
</control>
labels arent focusable so the id isnt as important. just make sure that its not a duplicate of a focusable control. id0 is usually where generic images are located so thats ok. or anything unique would be fine.
posx/posy is the position on the screen
width is how wide you want the text field. if its too short, the text will be truncated with "..."
align is the alignment of the text within the given width\
and you need to get a valid font. check other controls or open up font.xml to find a valid font.