Although, Alias Mother Jonez's write up is probably much more useful, here is something I wrote comparing Chretien de Troyes' "graal" story and Beowulf.
At first glance Perceval or the Story of the Grail (or Graal) appears to have a lot in common with Beowulf. In the case of theme and syntax they actually are quite similar. However, the religious history surrounding each of them differs almost completely.
Both Beowulf and Perceval are epic poems that have been handed down as an oral history. However Beowulf is a Pagan's tale, while Perceval is a Christian tale. Religion is cast out of Beowulf, whereas Perceval (up until a point in the story) is the model Christian knight; devout, humble, poor and full of other chivalrous virtues. The central story, with Perceval as the keeper of the Holy Grail, is wholly religious. However, after his experience with the Grail, Perceval finds that his actions have caused great chaos in his uncle's (who is king) land. He then makes a startling admission- that he no longer loves or serves God. Throughout the rest of the story Perceval is a man who is lost and needs religious counsel.
Now Perceval becomes a warrior like Beowulf, without a God and with the conscience of a warrior and nothing more. As Steven G. Nichols points out, "… Perceval's appearance mounted, in full armor on Good Friday, the day when Christians were supposed to throw off worldly garb and walk barefoot symbolizes for all to see the spiritual disarray of his soul."1
Another major difference between the two stories is that the author of Beowulf is unknown, whereas historians credit Chretien de Troyes with writing Perceval. Usually the author doesn't affect how a body of literature is received and comprehended. However it's necessary when determining historical significance.
Beowulf is more than likely fiction, for many reasons. One of the major reasons is that the author is unknown. This denotes the idea that the story was a common legend among Anglo-Saxons, and therefore is more than likely just joyful banter between people. However, in the case of Perceval, since we know (or think we know) who wrote it, it's easier to define how much truth lies in the story. Like Beowulf's dragon scene, Perceval has its unbelievable moments. However the author gives some more credence to the work as a whole.
Little is known of de Troyes. However, it has been established that he wrote Perceval during or around 1188 AD. This was a period of great religious turmoil, which included the fall of Christian Jerusalem. It has been hypothesized that due to the time period, the count of Champagne, his employer, told him the story to be recorded for posterity. The lineage of both the Count of Champagne and the Count of Flanders, to whom the poem is dedicated, gives the story some veracity. Both of these men belong to the "Grail family" or the descendents of Perceval. 2
It is important to point out that even today the actual history of Perceval is still in doubt. In most libraries Perceval still sits in the fiction section beside Beowulf. Due to the age of both texts, it's still largely left to the reader to dervive his own interpretation of the history of the stories, much like the content of stories themselves.
Nichols, Stephen G. "Picture, Image, and Subjectivity in Medieval Culture."
Modern Language Notes, vol. 108.4, September 1993
Article Available Online at: http://muse.jhu.edu/journals/mln/v108/108.4nichols.html
Baigent, Michael, Leigh, Richard, and Lincoln, Henry. Holy Blood, Holy Grail.
New York: Delacorte Press, 1982.