Using your phone or tablet
If you have an iOS or Android device you can download an app to control XBMC. I personally like Yatse over the official app on Android.
Using a web browser
To enable the remote control navigate to System → Settings → Services → Webserver and enable Allow control of XBMC via HTTP Make note of the port it enables, the username and password. You should then be able to enter the Ipaddress and port number (separated by a colon) of the XBMC (i.e. 192.168.1,120:8080) into a browser window of another computer.
more details can be found here.
Using SSH or to control XBMC from the command line
You can use xbmc-send. This may not be installed, but can be installed with this command
sudo apt-get install xbmc-eventclients-xbmc-send
A list of the supported functions can be found here
That is how SSH is designed to work, but after a little searching and testing the following does what you want.
After SSHing into the remote machine type the following in the terminal:
Then launch the program you want to display on the remote monitor, for example
more details available here.
Note the instructions above for Raspbian will likely work on Arch as well though I have not tested it.