Yes, they're available in English (and several other languages, I gather).
The three books about Arn and his adventures are called "The road to Jerusalem" (1998), "The Knight Templar" (1999) and "The kingdom at the end of the road" (2000), and they immediately became extremely popular by both ordinary readers and critics. And then there is a fourth book which is called "Arvet efter Arn" ("Arn's heir"), but I don't know if it's available in English.
They're written by Jan Guillou, a renowned (at least in Sweden) writer. He's written a lot of thrillers/action novels about a Swedish agent called Carl Hamilton as well.
You can find info about Guillou (in English) here:
http://en.wikipedia.org/wiki/Jan_GuillouYou should give them a go. They're really great! I hope the English translations do them justice.
If the film becomes a international success, I think this might turn into a new era in Swedish film making. It's the most expensive Swedish film production ever - 200 000 000 SKr (about 20 000 000 Euro).
I think these books has inspired you a lot Stefan, haven't they?