I wanted to know if there is a great difference between the Novel of a series and the manga of a series. In particular how different is the Shakugan no Shana and The Melancholy of Suzumiya Haruhi Manga from the Novel.

I don't know about the Haruhi manga, I didn't care for the character designs so I never really read it, but the anime is pretty much a "Suzumiya Haruhi's Greatest Hits". I highly doubt the manga could handle amount of content contained in the novels either. The novels are better than any version I've seen.

As for Shakugan no Shana... I wish I knew! ANN probably convinced me to avoid the manga, but I'll probably buy the novel.

[img]http://myanimelist.net/createimage/SirGir.png[/img]

Does anyone know if this manga is gonna follow the novels or is it just gonna go up to where the anime finished?

I don't think anything about where the manga will end has been publicized. As for me, I'd advice you to just read the novel and stay away from the manga. The original is always the best, al least, IMO. But I guess you can read the manga if you don't like reading that much. But as there are much less manga scanlated than the novel so... its up to you.

I actuallly started reading the manga first and then once I finished all the chapters that the scanlators had released(only 8) Iwas intrigued and I wanted more so I found that baka tsuki's website had the novel and were really almost up to date with Japan so I started reading it and I have to tell you like anime_lover122488 said the original is way better. I'm already at volume 6 and the story is awesome. Even if you don't like reading much you should make the effort cause its well worth it. Oh here's the page with the novel:
http://www.baka-tsuki.net/project/index.php?title=Suzumiya_Haruhi 😃

So pretty much whether it is Shana or Haruhi the novel is way different from the manga as it being the original so I guess it has more content or because you have read up to chapter 8 is the manga been similar to first novel and I guess some of the 2nd novel.