while working in VS2010 and creating SharePoint Content Types using CAML, i came accross an interesting issue. the issue was that when creating a content type, it was not showing up in the Site content Types page. Then after struggling a lot and almost exploring all the properties available, i found that there is a property called "Overwrite" and setting it's value to "True" i.e. Overwrite=True, makes the content type available in the Site Content Types Page.