When you type a WPA-PSK key in Windows XP, the characters that you type are automatically converted into a new binary key that contains 32 bytes (64 Hexadecimal digits). This binary key cannot instantly be converted back to the original key that you typed, but you can still use it for connecting the wireless network exactly like the original key. In this case, WirelessKeyView displays this binary key in the Hex key column, but it doesn't display the original key that you typed.
As opposed to Windows XP, Windows Vista doesn't convert the WPA-PSK Key that you type into a new binary key, but it simply keep the original key that you type. So under Windows Vista, the original WPA-PSK key that you typed is displayed in the Ascii key column.
this bit is interesting, is it saying some routers will not accept the key format to be in hex?
Each of the 64 hexadecimal characters encodes 4 bits of binary data, so the entire 64 characters is equivalent to 256 binary bits — which is the actual binary key length used by the WiFi WPA pre-shared key (PSK). Some WPA-PSK user interfaces (such as the one in Windows XP) allows the 256-bit WPA pre-shared key to be directly provided as 64 hexadecimal characters. This is a precise means for supplying the WPA keying material, but it is ONLY useful if ALL of the devices in a WPA-protected WiFi network allow the 256-bit keying material to be specified as raw hex. If any device did not support this mode of specification (and most do not) it would not be able to join the network