The following will get the DWA-140 working here in the US with most routers, using the Network-Manager in GNOME.

1. Check http://www.ralinktech.com/ralink/Home/Support/Linux.htm for the latest RT2870USB driver.
2. Open up a Terminal and "sudo bash"
3. "apt-get update && apt-get -y install build-essential wpasupplicant"
4. "cd /usr/src"
5. Copy the link for the latest RaLink driver and do a "wget" with it. Example: "wget http://www.ralinktech.com.tw/data/drivers/2008_0925_RT2870_Linux_STA_v1.4.0.0.tar.bz2"
6. Extract the driver. Example: "tar -xvf 2008_0925_RT2870_Linux_STA_v1.4.0.0.tar.bz2"
7. Change to the new directory. Example: "cd 2008_0925_RT2870_Linux_STA_v1.4.0.0"
8. "gedit RT2870STA.DAT &" and change the first 12 lines to the following if you're in the United States...

CountryRegion=0
CountryRegionABand=0
CountryCode=US
ChannelGeography=1
SSID=
NetworkType=Infra
WirelessMode=5
Channel=11
BeaconPeriod=100
TxPower=100
BGProtection=0
TxPreamble=2

9. "gedit os/linux/config.mk &" and change all the "=n" to "=y"
10. "make && make install"
11. "gedit /etc/modules &" and add "rt2870sta" to the list.
12. Close the Terminal, then try plugging in the device and see if its detected: reboot if it doesn't come up.