1. If you have a 7.72 server, you don't have to touch anything in sources.
2. You need 3 programs.
- sprite editor
- dat editor
- otitemeditor
3. Open with sprite editor your client/tibia.spr, and add whatever you want
4. Open clitent/tibia.dat with dat editor and reconfigure/add new items and new sprites
5. Open server/data/items/items.otb with your otitemeditor and verify all items.
6. From now your server may show "outdated items.otb", just ignore it.
7. Every player on your server have to download your new client. Otherwise they will get kicks by debugger.
Some programs are sprite+dat editor in one, like Blackdemon's Dat Editor. Doesn't matter for what version you download, newest are able to open/edit older files too.