By "window", I mean display a X application running on another computer to the terminal you are sitting in front of. X windows, which Linux uses as its graphical display, is capable of accepting connections not only from local applications, but also from remote (network) applications. Normally, access is turned off (to prevent obvious pranks/problems), but can be turned back on by using xhost.
So, for a simple example, open up an Xterm on your IA-1. Type 'xhost +' (or xhost + remote.system.name) to allow remote access to the X server. Then, log into a system that has some X stuff loaded (xterm being the simplest and most ubiquitous). If you used ssh, you can just start the application. If you used telnet, then you will need to 'setenv DISPLAY <ia-1's IP address>:0.0' for csh/tcsh or 'set DISPLAY=<ia-1's ip address>:0.0' for sh/bash, and then start your application. The end result is that the xterm will "run" on the remote system's processor, but display on your IA-1. This allows you to run programs that the IA-1 hasn't the RAM, storage or CPU speed to run locally.
For example, when I first start my IA-1, I:
1) start xterm by clicking the button
2) type 'xhost + whitetower' to allow whitetower to display applications on the local X server
2) type 'ssh whitetower (my freebsd server)' Connect to whitetower via secure shell
3) type 'who' Find out what the dhcp server assigned the IA-1)
4) type 'setenv DISPLAY dhcp0:0.0' Override the default X server environment variable, and point to the IA-1
5) type '/usr/mozilla/mozilla &' Start the app
Then, kick back and wait a few seconds for Mozilla to start. I've had it running for about a week so far, and since the IA-1 is silent and draws little power, I just leave it up.
As for xmms, it's the X <M>ulti <M>edia <S>ystem. Essentially WinAMP for Linux/FreeBSD. However, it must be run locally in order to access the sound hardware (until Midori supports the Network Audio System). I mount my music via SMBFS (windows networking) and play away.