I've narrowed my earlier post down to this: I have the router set to "WPA Personal" > "WPA Only", My laptop with XP and a Linksys adaptor prompt for a passphrase as should be, (and my iPod-Touch) but my sons PC has Vista installed and a D-Link USB adaptor, It prompts for "additional credentials" and the log on screen as used for "WPA2 Enterprise" (see this link scroll down and read the tutorial)
http://lts.brandeis.edu/techresources/connecting/wireless/securewireless.html#Vista
Now what am I supposed to do about that? It (router) has the latest firmware installed (Rev-C) It works fine except the Vista.