Need help creating custom vendors in mangos.

[Majex]

Title says it all, this is what I need help with. Also, MOST of the times I try .addspw (numberhere), it says the GUID can't be found.
A guide on how to make the vendors is first prio though! =)

[MentaL]

[x6x6x6x]

u need to get MDH it is the easiest way to add new things to your DB
than get the model id by choosing existing npc (can allso use creatures!) than run a search for it in MDH get the model ID copy it than make new creature edit to be vendor past the model ID make a buylist for it all in MDH than click "edit" to save,restart mangosd, and than use .addspw xxxxx ("xxxxx" means the id MDH has given you new npc!)