So you are saying you can issue a "iwlist wlan0 scanning" (assuming wlan0 is your card)
Do you use ndiswrapper or madwifi? You may have a broken Windows driver if it is ndiswrapper. I had a similar problem here and it took me a while to find out I had to replace the driver.
You could present a "lspci -v" here (just the wireless card)
Lets see if we can solve this