Tips for a practical joke

[Lorgon Jortle]

Alright,
My band teacher and I were talking today, and he knows I'm really into computers. He asked me if I would be able to change the ticker sign in our school lobby. I said that I truthfully had no clue, but I would love to look into it and learn.

My question is, how would one (not asking for specific directions) do this? Do they accept wireless signals or anything? I wouldn't want to do anything to the school computers (anything bad). I'm trying very hard not to seem like a wanna-be cracker. Where do you suggest I go to learn some of this?

Languages I know:

C++
Python
BASIC (like that's going to help...)

hey, thanks for any hints,

Lorgon Jortle