In order to verify what wireless card you're using in terminal: lshw -C network
That will atleast let you know if the card is even being recognized.
What type of network are you trying to connect to - WPA2 Personal, Enterprise, WPA, WEP, etc. I know nm-applet, the typical gui you seen on intrepid install, atleast for me, will not connect to WPA2 Ent PEAP networks. It would hose the computer every time it was authenticated.
Try to update your install through a wired network like previously mentioned. If that has nm-applet not connecting still your next method may be using wpa_supplicant with wext. I use NDIS for nm-applet but for some reason I can only make wext work for wpa_supplicant.
NDIS can be installed through Synaptic I believe. All you need to do is find the windows version of your .sys file from the driver zip you downloaded for it. I pointed the NDISWrapper gui to that file and it worked like a charm. Then I had to go through the trouble of making NDIS become the driver. I know there is a tutorial on that around here somewhere. If NDIS is actually installed and running on that lshw -C network terminal command you'll see "configuration: broadcast=X driver=ndiswrapper+Y" on the last line of the Wireless interface network entry.