Again the most recent newb out here asking for help ! I've been searching around and googling (definitely the two best tools ever) and although its possible to learn a lot from here and there, since the new multiworlds "thing" came out, no1 bothered on actually writing a tutorial on how to make it work properly. I wanted to implement this on my server and I had lots of problems... won't name them all here cause everytime I changed something (different plugins, different options, etc) I ended up having different errors. Mostly teleporting from one world to another would crash stuff and give errors. If there's someone out there who managed to achieve a "perfect" teleporting scheme with the default portals (the ones you build with obsidian, not using commands), I think it'd be a helpful thing to have a tutorial about it. It'd really help me and probably others out there A LOT =)
Maybe I just suck at searching youtube, but I didn't find a single tutorial for adding access to the nether in SMP. In fact, and maybe again it's just me, but you don't seem to have understood what the OP was asking for. He was not asking about generic tutorials for the nether, but instead about tutorials for how one adds access to the nether in SMP without players dying horrible deaths in the void or other problems that seem to come up when attempting to do this.
I've been trying to access nether in a server too. When I access nether from other servers, it's just a cave with netherrack...