Xnest is a cool little Xserver utility. You can use it like this:
twm -display :1 (or any window manager like twm that takes the -display argument)
and congratulations, you have a window managed by the twm window manager. Pretty cool.
Something else you can do is this, though I haven't tried it myself yet:
Xnest :1 -query <ip address>
This will connect you via the Xnest window to the remote Xserver, which I think is a pretty neat trick.