Please note that the two links in the 'Mapping for winxp' doco are out of date and these are the new links - 
http://download.kingpin.info/index.php?dir=kingpin/editing/maps/map_editors/QERadiant/qe4/ 
http://download.kingpin.info/index.php?dir=kingpin/editing/maps/map_editors/QERadiant/def/
Mapping for winxp is a good tutorial on haow to set up your Radiant.
One change I suggest is:-
In the QERadiant picture in the doco under ‘Views/Rendering’ 
you will see the 4th one along is selected (the one on the end) 
I highly recommend using the 3rd one along.