EDIT: These times are from 2010. For current information, click here!
Almost all churches (of all denominations) have some type Christmas Mass this weekend. Close to the Rival Hotel we have two churches one Lutheran and one Catholic. The Lutheran churches will have services almost exclisively in Swedish, while the Catholic churches offer services in several languages.
Katarina Church (Lutheran) has a late night mass on the 24th at 11.30pm, otherwise they have a Christmas prayer at 5pm. On the 25th they have Christmas Mass at 11am. These services are in Swedish.
The main Catholic church in Stockholm is called Katolska Domkyrkan and is just a 10-15 minute walk from the hotel. They have the following mass times:
12am- Midnight Mass (in Swedish or Latin I assume, no language given on website)
11am- High Mass (in Swedish or Latin, I assume)
3:30pm- Maronite Rite
If you are looking for a Catholic Mass in English, you will have to head to the downtown area... to St Eugenia Church. They have a midnight mass on the 24th and a mass at 6pm on the 25th and 26th. All three in English!