If your serious about storing then drain all fluids, ensure all seals are water tight, put the car on axle stands and romove the wheels and cover it with a high grade but breathable sheets.
A friend did none of the above when storing his old Porsche and after 5 years of sitting still turned a £20k car into a £5k non running good for parts only Porsche. His only saving grace was that he removed the private plate from the car which was valued at £10k+.
Blimey, that's worrying! I've just bought a car and stuck it in the garage with the intention of only getting it out in the summer for a couple of thousand miles per year.
I would not worry about it too much, the Porsche was store outside and had about 1/2 inch of moss on it and he had to literally cut the cover off the car when he finally decided to sell it.
My wife used to have an old mini which used to do 800 miles a year and it ran without any faults ever
Sorry I've no contacts for this myself, but if I was looking for one I'd be heading for the Pirate Bay or some other download site rather than pay hundreds of pounds. I did find one on there but it was for North America and Canada - I bet with a bit more searching on torrents one could be found.
After a quick google, this guy sells them for £35:
BMW SAT NAV MAPS FROM *** £20 ***
if you can't find a free download?