Unfortunately the drivers for this wireless usb card is not included in osx and to make things more frustrating the driver is not provided for osx on the linksys homepage. But do not worry there is a solution!
The chipset in WUSB600N is made by Ralink and is called RT2870 and on the Ralink webpage you can download the driver. Go ahead and download it and install it reboot your computer when it tells you to.
That should have been that but for some reason the WUSB600N the product id for WUSB600N is not included in the kext file. To be able to use our card we need to edit the /System/Library/Extensions/RT2870USBWirelessDriver.kext. Open up the file in your favorite editor. And search for Linksys you should find a section looking like this:
Linksys - RT2870 - 1 CFBundleIdentifier com.Ralink.driver.RT2870USBWirelessDriver IOClass RT2870USBWirelessDriver IOProviderClass IOUSBDevice idProduct 112 idVendor 5943
This is another cards from linksys that are included in the driver that uses the same chipset as our card. So now you have the option of either edit that entry to have the product id 121 (0x0079 in hex) or add your own card after. Since just editing the existing card could break another card I recommend adding the code below just after the instead
Linksys - RT2870 - WUSB600N CFBundleIdentifier com.Ralink.driver.RT2870USBWirelessDriver IOClass RT2870USBWirelessDriver IOProviderClass IOUSBDevice idProduct 121 idVendor 5943
Now you just have to reboot and you can enjoy your WUSB600N card :).
The card is handled through Ralinks wireless utility that can be found in you application folder.