I'm fairly sure ralle based the resource sections off the forum sections, since they are counted as posts and show up on searches. Though he could have just integrated them, not based it upon them. As for the other question, the info is stored in MySQL tables, though the storage method shouldn't matter too much.
As for getting a maps data, you're going to need a custom program that is compatible with your server which can manipulate MPQ files. Writing a script which does that in a server language like PHP would be fairly difficult and probably not worth it. You can look at such libraries as
StormLib and
sfmpq and do it in C++.
Once you have that program, you're going to need to make something which can parse the maps files in order to get the info out of them. Things like maps name, tileset, author ect. This could be done directly on the server and shouldn't require a program for it. As for BLP images (map preview, skins, icons), you're going to need to make another program which can read BLP and convert it to a format viewable by browsers.
If you have these utulities it's very easy to develop a rough draft of this system. I've done it so myself (a little past a rough draft). Though I know ralle does not like to share these utilities for obvious (and understandable) reasons. There are also other ways to develop such a system, but this is how ralle does it and it's probably one of the most elegant solutions.
Sadly, if you do not know where to start you are going to have a long way to go.