I don't have the XDK but there is a solution with the IOTDK for using UART 0, it is just currently broken. It should be fixed shortly. Once that is accomplished you should be able to talk to it using termios in C or any of the other mechanisms normally found in Linux environments.
That is my theory anyway and I'm clinging to it. Desperately.
I have the same problem is there any way to use UART using IOTDK im not able to use SPI its throwing errors.
There are some examples about WebServer that you might find useful in the Arduino IDE.
Regarding the XBee module, you shouldn’t have problems to interface it with the Galileo board. There are some threads taking about the XBee module and also there are some test reports that you can check here: Intel® Download Center. You can check them as a starting point.