This site is the best resource for info and help writing plugins for vb3 and vb4. It is also the best resource for vb5 mods. VB3 and 4 are easier to write for since the documentation is there and there is a plugin system. VB5 is more of a challenge, but once you understand the API, it is not impossible as some might think. Here is a document to help understand how the vb5 backend works.
https://vborg.vbsupport.ru/showpost....47&postcount=7.
Here is documentation on vb5 API.
http://vbulletin.wayneluke.com/api/