To start with the major differences between media ideology and spin are that (1) ideology is the philosophic, governmental and intellectual presupposition that creates the hegemony (dominant thought) behind the media whereas spin is what influences the statements of the news. While both ideology and spin "shape" the statements reported in the news, ideology is widely accepted within the populace whereas spin is an attempted hidden manipulation of the populace. Also (2) ideology has had wide currency from the beginning of news reporting whereas spin is said to have begun at a precise moment in time in 1984 following the Reagan - Mondale presidential debate.
Ideology is born of the presuppositions of governance and opinion generally (though not ever universally) agreed upon within a country. These presuppositions (assumed beliefs that are often not debated or contested) are handed down from the elite groups that govern and that hold intellectual authority within a country, for example, the Supreme Court, universities, etc. For instance, in India the elite still adheres to degrees of the ancient caste system so news reporting is influenced by the presuppositions stemming from this ideological stance based on religion and cultural beliefs. Another less dramatic example is the dominance of football as a sport in the United States, which takes over television programing at least one night a week and on major winter holidays. This stems from the ideologically accepted belief that football is of inestimable importance (as do the players salaries...).
Spin is born of the moment as one person's or one group's effort to alter the general populace's perception of an event or situation. Whereas ideology is based on general agreement, spin is based on private opinion and need and aims to manipulate what the general populace will agree to pertaining to one person, event or situation. Spin doesn't usually aim for ideological changes or agreement, spin aims for reconstructing how people think about isolated instances of behavior, problems, events, etc.
[For more information, see MediaKnowAll.com and The Anatomy of Spin: Causes, Consequences, and Cure by Kenneth S. Hicks, Rogers State University.]