http://www.melbourne.wireless.org.au/maps/clickmaps/800x800clickmap2-6.php?

Browse around and find your location and click on it.  It will give you a
"clicked latitude" and "clicked longitude".  You can then paste the
coordinates into your new node, or if you haven't created a node yet, click
on "create node here".

Behaved strangely under Firefox - kept moving in the wrong direction!
Worked perfectly under IE 6SP1.