PCSX2 .pnach file
Extract this file to your pcsx2 cheats folder (make sure cheats are turned on in pcsx2. this works for build 8 only.)
If you installed PCSX2 1.4.0 like that one YouTube guide says to do then make sure you put the pnach in Documents\PCSX2\cheats and not Program Files\PCSX2\cheats.
For PS2
Netslum Patcher
Download the netslum patcher files and extract them. Copy the build 8.13 iso into the same folder as the extracted files, then run patch.bat and follow the instructions. The game client will then be directly edited to connect to the netslum lobby.
Area Server
CC2 Server // Netslum Server
Download and install the CC2 server (click "ダウンロード"), then download the Netslum Server and copy the file into the folder where you installed the CC2 server.
VirusTotal scan of NETSLUM SERVER.exe for the curious among you.

Other Links

Netslum's Friends

These guys host the latest version of The World 2D and are working on an MMORPG version of The World R:2 in Unreal Engine, they're great people, give them some love!
The World V:R
An ambitious project aiming to recreate and re-envision The World in virtual reality.
Dothack Network
Probably the largest english speaking .hack// community on the internet. They have a discord server full to the brim with people who love .hack//.