To get started, you can begin with just OpenZone and my sample textures. The sample textures are available here, and there are hundreds of textures to get you started:
http://sourceforge.net/project/showf...ease_id=276191
I've also released some sample zones so you can see what is possible with OpenZone:
http://sourceforge.net/project/showf...ease_id=333409
If you want to make dungeons, you will also need Dungeon Builder. It exports standard 3DS-Max (.3DS) files that you would import with OpenZone (Dungeon Builder really has nothing at all to do with EQ and can be used for any purpose). Dungeon Builder 1.8 is available here:
http://sourceforge.net/project/showf...ease_id=333537
EQZoneViewer is great for looking at your exported zones for the purpose of making sure that they're what you want, but it's not required. It's not being updated anymore, but you can find it here:
http://www.eqzoneviewer.com/
If you want to make your own textures, you can use a picture editor, but a better solution is a dedicated texture creator that can make seamless textures. I use Texture Maker:
http://www.i-tex.de/
OpenZone is limited in the quality of the zones and objects that it can create, and an external tool like GMax is helpful if you want better. OpenZone can import standard .3DS files so any tool that can export to them should work just fine. OpenZone can also import Quake III levels, but it doesn't import everything about them, like multiple shaders (only transparency gets imported).
S3DSpy is useful if you're making weapon files (e.g. a gequip.s3d replacement) rather than zones. S3DSpy is basically like a WinZip for .S3D files: that is, it's a generic archive management program that lets you add, remove, rename, etc. files in .S3D archives. S3DSpy 1.2 is available here:
http://sourceforge.net/project/showf...ease_id=315328