I lived in the IOM for 3 years back in mid 90's. Nice place but a week is a hell of a long time depening on your circumstances eg have u young kids etc.
Not a lot to do there for a full week - I'd suggest 3 days max. Can't remember the name of any hotels but Douglas is the best place to stay as u can recah the rest of the island from there within 30 mins by car.