Try googleing Just "X chat scirpts"

yes it uses perl, along with python, tcl, and ruby, but again I have yet to stumble across a script like !topic on the official scripting page or any other place for that matter. The closest thing I have found is edittopic located here: http://orvp.net/xchat.php

You also will have to install PERL,TCL,RUBY or PYTHON
As they do not come preinstalled on x-chat

One thing I would like to point out is that since this script has :#: it is not channel specific so in order to do that do :#channelname:. If you don't select a channel you want it will change the topic in everyroom you an op in.

ON *:TEXT:!topic *:#channelname: {

That will make it only fire off in a room that you want it to.