Sorry, I accidentally deleted the lxde thread, (on mail where I just use POP3) so headers may be broken for some of you.
Anyway, ScientificLinux forums have a post about building lxde. It is time consuming, but if you really want it....
It's using Fedora 14 as the version and has links to necessary rpms.
http://scientificlinuxforum.org/index.php?showtopic=759