We had a week in Ullapool a couple of years back, and it is a very very beautiful part of the world.
If you are uncertain where to stay, you must stay at Point cottage. It is a small friendly guest house, with just three rooms, but it has the most superb position in Ullapool. It is right down at the end of the point, where the ferries turn to go out to Stornaway, and you can lie in bed and see right across the loch, and watch the ferries passing. It is wonderful.
It is a very peaceful little town, not a lot there, just some gift shops, pubs and resteraunts, and a small harbour. There are lots of nice walks though, and lots of beautiful places to visit in the Scottish Highlands, and it is just so peaceful that you cant help soaking up the atmosphere and relaxing.
The weather wasnt too brilliant when we were there, but it is supposed to have its own micro climate, warmed by the gulf stream, and on the whole they are supposed to do quite well for weather there!