Thanks johnrw. I followed your instructions but it did not work.

I rmmod the kernel driver, updated the two ndiswrapper packages and reconfigure the wireless network. The wireless light still did not come up. What's more, the wireless netcard was not found when I used dhcp to configure the network. It showed:

Sending DHCP broadcast from device eth0SIOCSIFFLAGS: No such file or directory
Operation failed.
Failed.
Hit return to exit

Then I checked with lsmod. It said:

bcm43xx 417768 0
firmware_class 11648 2 pcmcia,bcm43xx
ieee80211softmac 27008 1 bcm43xx
ieee80211 33864 2 bcm43xx,ieee80211softmac
usbcore 109084 6 usb_storage,uhci_hcd,usbhid,ehci_hcd,ohci_hcd

I was totally confused about this. Could give me some more suggestion?