check out the video tutorial page in the section of the forum, its pinned as important. in the section called "other" at the bottom, theres a tutorial about making world spaces. haven't checked it out yet.
heres a link to the download page for it. http://www.fallout3nexus.com/downloads/file.php?id=3541
just had a look in the RAR file and it seems to be in the form of a HTML file. not a video but its got lots of screen shots and details so it looks good.