¡Oh, Sonic, oh Sonic! Lucha contra el doctor...
¡Robotnik, Robotnik! Y contra su escuadrón... 
That's how they translated it? Seriously? *giggles*
It's the AoStH opening. They added lyrics to it. "Fastest Thing Alive" wasn't used, so the AoStH opening was used even in SatAM.
AoStH was bought by the channel Tele 5, which belongs to the Italian company Mediaset, so, in those years, many openings in Spain were Italian openings (sometimes in other series) with different lyrics to match the new series.
They took the Italian opening of "Widget":
http://www.youtube.com/watch?v=RsVeJY_dmvQ
And turned it into "The Adventures of Sonic the Hedgehog":
http://www.youtube.com/watch?v=vgntHoS-6aU
The Sonic lyrics translate to:
(Hey kids, we've got a champion we love. Sonic!)
He's a wonder, he's fast as the wind,
a way to freedom.
His goal is to free his planet
restoring its serenity.
He's a courageous fighter,
a real friend.
He's generous with people,
and he will never change!
(He's something special)
He dreams some day there won't be tyranny
in his bright and happy world.
His partners are also his warriors
and they will stay with him till the end.
Oh, Sonic, oh, Sonic!
He fights against Doctor
Robotnik, Robotnik!
And his squadron.
Oh, Sonic, oh, Sonic!
There will come a day
When your planet will be freed.
Oh, Sonic, oh, Sonic!
They will never get you!
Oh, Sonic, oh, Sonic!
You'll always beat them!
Oh, Sonic, oh, Sonic!
Everyone will acclaim you
And your good works
will have a reward.
You're astute!
You escape from all the dangers every time
Like no one!
You always know how to defend your life...
Oh, Sonic, oh, Sonic!
He fights against Doctor
Robotnik, Robotnik!
And his squadron.
Oh, Sonic, oh, Sonic!
There will come a day
When your planet,
When your planet,
When your planet,
will be freed.
(Sonic!)
As a curious fact, Sonic and Tails's voice actors returned for SatAM and for Sonic X, and the dubbing director in AoStH and SatAM, Carlos Revilla, also played Dr. Robotnik, and he's best remembered for being Homer Simpson's voice in Seasons 1 to 11 before he died in 2001 (and, so, he couldn't return in Sonic X, sadly).
Sonic's voice in Sonic Underground (the first voice of Shinichi Kudo in Detective Conan/Case Closed) also portrays him in Sonic Generations, this time, trying to sound more like the Sonic X voice, and less like his "mondo cool" performance in Sonic Underground, which only suited him in SU, but not in any other media.