Things to see in athens in 2 days

We are traveling to Athens in mid January 2010 and are staying for 2 days in hotel Divani Palace Acropolis. Can you suggest for us what to visit, how to reach main attractions, where to buy best souvenirs, where to find good restaurants, what is the weather like in January, and is it easy to see makrigianni, plaka and monastiraki areas on foot?
And also we would like to visit National Archeological museum. How can we reach it from our hotel.

Thank you