If you are looking for information on getting to and from the marina for the trip, you need to look at the other webpage "Athens transport".
If you want to stay in Athens, then CUYC has used the Student Travellers Inn in the past. It is clean, central and cheap.
To get into Athens central from the airport, take the metro or bus X95. See the bus map (which also has metro lines) on the other webpage "Athens transport".
To get to any islands by ferry, you will need to get from the airport to Pireus (the port of Athens) and get a ferry or hydrofoil. There is a direct bus X96 which does not go through the centre of Athens. A map of Pireaus is shown below to help you find the ferry/hydrofoil terminal: it is at E9 quay (E9 extends round that curve too) for Aegina/Poros/Hydra. You can buy the ferry ticket at the port.. The bus takes an hour, you should allow an hour to find your way around the port, and the ferry takes 90 minutes (the hydrofoil is faster). The ferry timetables have not been published yet, so please don't ask us the times: we don't know.
The best way to get to Pireus is the X96 bus from Athens Airport to Pireus: there are lots of bus stops around Pireus harbour, you want the bus stop No.4 marked on the map below, or the Metro Station (also called ST.ISAP on the X96 bus map) .The bus runs 24 hours a day and is every 30 minutes or 15 minutes, depending on the time of day.
If you want to get a good guide to catching ferries at Pireus, buy the 2012 "Greek Island Hopping Guide" (to be published on Feb.12th) which also has an excellent guide to Athens and its museums and ruins, as well as all the islands.
If you want to visit Athens before or after the sailing, you will want to use the Athens metro. If you are not going into Athens at all, then you will not use the metro, just the X96 bus.
Note that from Pireus to the Airport you need to change from the Green line to the Blue line in the middle of Athens. There is also a special fee for the metro to the airport: everywhere else is a flat fee, but the airport is extra.