On this website (made in 2008) you can find a lot of basic information about how you should plan a trip to Athos. Beware, some of the information is outdated. And you might get the impression that is neccesery to go the Pilgrimsbureau in Thessaloniki first, but that is not the case. As soon as your reservation is confirmed by telephone, fax or e-mail, you can go directly to Ouranpolis and get your Diamoniterion over there. (today I was told that you also can use this e-mail adress: firstname.lastname@example.org).
The link to the KTEL bus company is not working, and today I was not able to find a new adress. My advise is not to buy the (expensive) Zwerger map, because the Road Editions map looks better and is more up to date.