it all depends at what stage you are at.
1) Cant code at all
2) can code but not in C++
3) can code in C++ but not for the xbox.
people in the first section should buy a book or take a course, online tuts are very rarely complete enough to teach. once they have learnt to code then move on to section 2.
People in the second section could check out some of the C++ and Direct X tuts available on the net. once they can code in c++ move on to section 3.
People in the third catagory should just check out the sample files that come with the dev kit.
Hope that helps.
oh
http://www.xfactordev.net/ has a hello world 'tut'