The following lines in /e/n/i worked and wireless is now running (I am connected over it with ssh), so the hardware is fine - though it is the onboard card that is working, and the USB card is still not!!
sarah@debian-wheezy:~$ cat /etc/network/interfaces # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback # Bring up wireless auto wlan0 iface wlan0 inet dhcp wpa-ssid myssid wpa-psk <passphrase> myssid is verbatim, although it is not, of course, my SSID. So can I make /e/n/i ask for the passphrase at each connection? And what do I do about the possibility that the wired connection might be connected? Lisi