In reply to salix:
I think this topic somes up every year, and there is always loads of advice, both good and bad. I've been in Edinburgh 4 years now with no car, and after a fair few mini epics (many without even getting to the hill I was aiming for) I can safely say that finding partners with cars is the best option.
I am a keen hitch hiker, but in the Highlands in winter its a bit of a tall ask. It also means that the 3 hour drive to the start of the walk in requires a day set aside, as does the return. It shouldn't take that long but sometimes it does.
Public transport always seems to get you close but not quite there, and again takes twice as long as a private car.
Joining a club might work, I've never really tried it. The best option I've found is making a plan with someone on UKC or at your local climbing wall! Sometimes you even become friends afterwards.
Without a private car, any Highlands winter trip becomes an adventure, which is really cool, but not good for getting much actual climbing done, and also very bad for getting back in time (and a fit state) for work on Monday.