The easiest thing to break those lines loose are flare wrenches. Some people call them line fitting wrenches. Either one is right. Put a pair of those on there, and squeeze them together. It will pop loose, rust or not. I've done it with and without them, and I'll never do it without them again. Sears stocks them in metric sizes, and you can buy just the one you need once you know what size to get.

Just make sure you have all the copper crush-washers you need to put it all back together.