There are serveral ways to get your ip addres.

1.) goto Tools --> Connection Manager.
From the appMenu, select "Internet Connection", then IPAddress

2.) Another App, called "WiFiInfo" is here:
http://www.anderenen.de/anderenende/maemo.html

3.) Another option is the IPHome applet from here:
http://www.mulliner.org/nokia770/

4.) or you can make your own, with this simple python script (requires Python runtime)

-------------[ ipaddr.py ]-------------------------

#!/usr/bin/python
import gtk
import commands

window = gtk.Window(gtk.WINDOW_TOPLEVEL)
window.connect("destroy", gtk.main_quit)
window.set_title("IP Address")


textview = gtk.TextView()
textview.set_editable(False)
textbuffer = textview.get_buffer()
ip = commands.getoutput("/sbin/ifconfig")
textbuffer.set_text(ip)

sw = gtk.ScrolledWindow()
sw.add(textview)
sw.show()
textview.show()

window.add(sw)
window.show()

gtk.main()