Hi
There is a train from the airport to the citycentre. Very handy, takes 20 minutes.
http://www.arlandaexpress.com
There is also a bus service from the airport.
http://www.flygbussarna.com/en/default.asp
We visited Stockholm in August and stayed this hotel.
http://www.eng.stallmastaregarden.se/
It was really nice, just outside the main hustle and bustle, beside an inlet from the sea. The above mentioned bus service stops outside the hotel. We booked with hotel.com or one of those websites, which gave us a good deal.
It will be dark and cold in the end of November, but with hat, gloves and good shoes you will be OK. As they say in Sweden "There are no bad weather, only bad clothes".
Will you be there for Sunday 2 December? First of Advent is a big thing in Sweden. Almost everyone, even those who dont normally, go to chuch to sing the traditional carols. There will also be Christmas markets around. You definately have to visit Gamla Stan, the old town, they would have Christmas markets on around that time.
The transport system is handy and easy. There is also a Stockholm card which includes travel and entrance to museums etc.
Skansen is a nice place to visit. It's an open air museum, with buildings from different areas of Sweden, and also animals. [broken link removed]
Have fun!
PS. Dont worry too much about the prices, it's not hugely different to Dublin.