When you say geraniums I guess you mean the annual pelargonium's that are often called geranium's.

If so i over winter them in one litre pots on indoor windowsills with plenty of light. I give them a hard prune 3 weeks or so before they're ready to go outside again in late spring once all fear of frosts have gone.

You could also overwinter them in an unheated green house or garage with plenty of light. You may lose them if it gets very cold and be sure to keep them only just damp. They'll rot if they're kept too wet

I have tried in the past to overwinter mine in cold frames in a sheltered position outside and never survived. I am afraid I am going to do the same again this year as my wife will never allow me to bring them inside. Lets hope we get a milder winter.

Yes, I'm afraid I've never had success with pelargoniums in unheated frames/greenhouses although so9me people I know say it's worked for them

If you only have a few try planting them in a trough - they take up a bit less room up than in pots. Keep them on the dry side in a good light - the cooler the room the drier they need to be. As they are semi-succulent its surprising how much dryness they will survive. A sill in an unheated spare bedroom should be OK for instance.

I hauled all my pelargoniums and their pots up to the (very light) loft last winter, and allowed them to dry out quite substantially. I still lost 80% of them in our truly awful weather - probably due to the fact that our loft insualtion was too effective, and it was no better than leaving them in an unheated greenhouse. If you have a cold spare room and a garden-loving wife/husband, it's your best bet. (What a shame, Costas - better luck this year)

I usually manage to keep mine huddled together in an unheated greenhouse, but it is generally fairly mild here.

Ours are on the bedroom window sill which is quite wide but they are not a pretty sight. However it did work last year and all survived. They never did when left in the greenhouse.