The Tollan first appeared in series 1 episode 'Enigma' after the SGC saves them from a natural disaster on their home planet. (Um, I think it was a volcano, as in it wasn't like an attack or anything.) After that they were obviously anxious to leave Earth, but don't before Carter figures out that they have basically grasped the theories behind quantum physics. This means that they are way, way, way ahead of the human race, for the closest we've got to understanding that sort of physics is the cat-in-the-box idea. (Schrodinger's cat)
Meanwhile, there's the problem of where the Tollan will go, since their planet is uninhabitable. They allow the humans to use a device which sends a message to the Nox. A Nox member comes thorugh the Stargate, saying that they would take the surviving Tollan to their planet. The Tollan accept this, as their conditions for be re-homed were that a race had to have a technological level which is equal or supperior to their own. The Nox have such technology, albeit that they otherwise resemble fairys in my opinion. The other problem comes from US people who don't want the tollan to leave without doing their standard tests. They get passed that because it is Daniel who allows the Tollan to go through the Gate to the Nox homeworld, on the principle that he is a civilian, and therefore cannot be court-martialed.
On appearance, the Tollan are humanoid, though whether their ancestors arrived on their planet after Goa'uld transportation I don't know. Considering they are at a extremly high level on technology, where that of formerly Goa'ul ruled worlds are not, I am thinking that they are human, without being of Earth origin.