you need the modded html- and js-file too. (:
and of course copy over a picture for your avatar since it's not loading correctly for sms conversations from id. ^^

and yep. it's kind of slow.
but that's because of the poor javascript performance of the mozilla browser engine which is used for displaying those conversations.
i posted something in the js speed comparision thread that mozilla is working on "jaegermonkey" which should speed up js performance to a level like webkits (tear, midori) and safari (well-known from iphone).

right now mozilla is using an engine from 2007 (!!!) which tries to find loops in js-code to make it faster.
if it doesn't find any of those - it's slow as hell.
other browser are using a much easier way which pays off more often:
they are building blocks in js code and speeding up the calculation. (this is where jaegermonkey will step in)

i'll make some zips.
programming an app for doing this replacement isn't hard at all because the only thing it has to do is copy the content of a directory in MyDocs (where you have access with usb and normal user) to the html-folder (where you have to be root to change things).

i think if some more people would be interested in modding conversations a programmer like VDVsx (who has made the bootscreen-app which is doing nearly the exact same thing as this app should do) could write a small app for doing this.