- Where and how can I download the in-game font of SC ? Not the game's title or texts (chat, transmission,...), i mean the font of the buttons.
- How to insert the "transition scenes" to campaigns, like Blizzard's campaigns ? And like the demo, when we click the "Single Player", it automatically loads the campaign ?
- How to make permanent hallucinations, broodlings and permanent energy for all spell-units (ht,ghost,etc) ?
Thanks for any helps !

Permanent hallcinations are impossible.
Each hallucination will die when their timer is up.

"Normal" campagins only consist of maps and you cannot directly implement those things.

I have the impression that you want to mod. Or at least, you need to mod and change Starcraft's campaign to have access to that things.
This topic may should be moved to modding assistance.

The Tahoma font looks like the text your referring to, at least its the closest I could find. For permanent energy you can accomplish it via a preserved Modify Unit Energy trigger. As for permanent broodlings, there's a way to do it but I don't seem to remember how and I can't find the previous topic about it...

I agree with Ahli, if you want to make/edit a campaign with those features you'll need to mod starcraft. If you want to learn then I suggest you refer to the first bullet in this post.

1) I believe the texts is Verdana.
2) That will not work for multiplayer, but there is a trigger that says load next scenario.
3) Hallucinations cannot be permanent, unless modded. Broodlings can last forever by creating it (Not with Properties). Energy of regular units can be permanent by using the modify unit energy trigger along with preserve trigger.