I have exactly the same issue as an earlier poster. My netbook shows connection to my router but is unable to connect to the internet over the wlan. It will connect over the lan. My laptop is working properly on the wlan.
I am running WinXP; I have windows firewall off; I have tried Zone Alarm off.
The netbook shows Destination Host Unreachable if I ping anything.
Ipconfig/all shows Host name Netbook, Primary DNS Suffix blank, IP Routing not enabled, WINS Proxy not enabled.
Wireless adapter shows Connection sspecici DNS Suffix : blank, it is an 802.11b/g mini card address 00-1D-92-C4-29-7F and DHCP disabled. IP Address 192.168.1.1 Subnet 255.255.255.0 and no default gateway.
Needless to say, it was working but I have not changed anything except to try resetting WPA/PSK TKIP