You can always get a car cover.
Call your city hall to find out the exact laws on animals running loose in the neighborhood.
I've read about some products that are spread/sprayed on the ground that cats don't like. Check with some local pet stores or online.
Get an estimate for repairs from BMW and ask your neighbor for reimbursment (be sure to show him/her the picture of the cat in the act of doing the damage). If the neighbor doesn't pay, get the work done and ask again for the $$, in writing. If still no $$ then file a small claims suit in your local court.
You can also buy/rent a small animal cage trap and try to catch the cat and turn it over to your local animal control authority, especially if it doesn't have a collar or tags.
2004 E60 530is, Delivered 12/12/03, TiSilver/LGrey, PP, SP,PS, PDC, ACC, FRS, Step, Xenons, clear bra, body colored rear inserts. (Retired, 1983 henna red 320is)
2004 Corvette Z06 Commemorative Edition