Send response to client

[Christ Schlacta]

is it at all possible to send a message to a windows 7 or windows vista 
client that the client is guaranteed to see when authentication is rejected?
more details:
wireless WPA2-EAP-TLS on a Ubiquiti PicoStation 2 firmware 5.3.2 (I 
believe it includes some form of hostapd, but I'm not sure which version)
Freeradius Version 2.1.9
Clients running Windows 7 or Windows Vista with no special software 
installed.  the procedure is OS, Wired Driver, ethernet cable, Windows 
Update once for drivers, Wireless certificate, connect to Wifi, (Note 
this point) finish updates.

It's at the Note this point point that I want the clients to be able to 
recieve a rejection response with some level of certainty.  what users 
add to their system later is welcome to break it, if they're willing to 
deal with it.