Installation is easy:

1) Make sure you've got php3 or php4 working
2) Make sure apache is set up to recognise .php files
3) Untar the distribution file into your page
4) give write permission by the httpd on mlchatlog
5) edit mlchat.conf to fit your needs

If you want it as add-on:

1) Just say so in mlchat.conf!

That's it! Have fun:)