chivalry

that's always hard to say, it will also vary according to the timeframe, but i would say in the early days there were only a few black sheeps while in the last years of knights, when gunpowder replaced their importance on the battlefield and became robber-knights, chivalry was as good as dead. although the idea still survived into the renaissance and beyond.

Chivalry as a concept derived from the word for a horseman and by extension a knight. (French 'cheval' = horse). The term was in use already in the early 13c. and by the 14c. was being extended to refer to courtly behaviour.

In European literature there was definitely a tradition even before then (I'm really only familiar with stuff back to 1160 or so). What that shows is the ideals that later came to be called chivalry being reflected in epic court poetry. Was it actually practiced? We just can't know - but the mass of literary history we have left certainly suggests so. Stories like this would never survive / succeed if the audience would not believe them to be true or possible.

The birth of Chivalry has also been traced and linked back to earlier Germanic tribes.

Literature of the period, or more accurately, oral tradition in the early Medieval era can be traced to characters such as Beowulf, Arthur, and Rolland.  These men were the quintisential epitome of all that a mounted knight should strive to become.  The ideals, as Shadowedrelm stated above, were passed down to the Medieval era from Germanic peoples, as with Beowulf and Rolland. (although Rolland was from Britanny and thus a Briton or Celt, the story is nonetheless Frankish).  The tradition of chivalry can be sourced to the early years of the Germanic and Celtic period. 

in one of by books I foudn a knights-oath:

1. I vow to believe all teachigns of the church and to keep its commandments.

2. I vow to protect the church.

3. I vow to protect the weak.

4. I vow to love the land of my birth.

5. I vow to never run away from an enemy.

6. I vow to figth the heathens to death.

7. I vow to fullfill my duties against my liege, as far a they are not against gods commandments.

8. I vow never to lie and to stand to my given word.

9. I vow to be frank and generous to everyone.

10. I vow to always fight for law and against injustice and evil.

"how instermental was the church in the ideals of chivalry"

The Christian Church was trying to stop (or at least to lessen/somewhat control) violence. The Truce of God, for example, which dates from the eleventh century, was meant to curb violence through suspensions of hostilities. In large part, I believe that the church took Germanic views of the ideal warrior and infused them with Christian virtues to form chivalry. Many of the values and virtues of chivalry preexisted but were then Christianized.

"was it common thought or just for those in the 'high towers'"

In practice, I think that the appearance of chivalry in so many oral and written stories shows that it was on the minds of Europeans of the day, even if it was highly idealized. So that would mean that it was common thought. This does not mean it was necessarily practiced very often, however. I don't really think that the sources that are currently available can provide us with how much the chivalric code was followed in actual practice. I do, however, think that as an ideal, there were those who tried to follow chivalry.

"Not that I disagree but under that premise then the themes of much of todays pulf fiction should be on the minds of the inhabitants of our time."

That point wasn't really explained very well. I was thinking more along the minds of popular movies of today. A good example is gangster movies. This may not be your favorite type of movie, but most people today have a good idea of what a gangster is. It's part of popular American culture. The images of gangsters in movies are not always realistic, but they're a sort of idealized picture of what a gangster is, and these images are based upon the way that actual gangsters did act and what they did do.

Stories (both oral and written) were one of the major forms of entertainment for medieval people, similar to movies today. What I'm saying is that the romanticized stories that we have of chivalry were idealized and not completely accurate, but they were based on reality. Popularity doesn't make something real or true, but in the case of chivalry I do think that despite the elements of idealism, there was a definite basis in reality in which knights actually did practice and live by the codes of chivalry.