In reply to kieran b:
I've left cars parked up for months at a time. Ideally it's best if someone can drive the car regularly for you.
Before you park it up, give it a good clean, and be sure to clean the underside and the wheel arches. Get all the muck, salt or whatever else off. Clean all the brake dust off the wheels.
The car will get damp inside, especially over the winter. If I couldn't get someone to drive my car regularly, I'd get them to run a dehumidifier to help prevent condensation build up. You could try those condensation traps people use in motor homes or caravans as well. These will need emptying and topping up with new crystals regularly though. Mould can/will grow on the fabric quite nicely thanks to condensation.
If the battery is good it might be ok to leave it on the car. There's no guarantee, so it's up to you. If you do disconnect it, your alarm won't work, which may be a problem. Depends on where you park it I suppose.
I've just put a car back on the road which had stood for 5 months. I had to recharge the battery, sort the brake calipers which had a couple of stuck pistons (although they were sticking before it was parked up), and sort out an idle control problem. Luckily my brother is a whizz with this sort of thing, but without the right diagnostic gear you could run into problems.