I\'m using Eclipse Helios on Ubuntu 10.04, and I\'m trying to install CDT plugin on it. I download it from here here.
And then I go to Install New Software<
I was having this same problem and found the solution in the anwser to another question: https://stackoverflow.com/a/1951132/425749
Basically, installing CDT does not install a compiler, and Eclipse's error messages are not explicit about this.