I have been thinking about this for a while. It's really not a technical problem, but a people problem, one which lots of people in industry run into.
I would suggest that you not give him the data. Your instincts seem to be ruling against it, and in a case like this I would trust them. The trick is to refuse while being diplomatic about it.
The first thing to consider is the actual ownership of the data on the disk. If it belongs to your firm and not specifically to you, you can cite your stated company policy about this sort of thing; tell him that the firm has just recently cracked down, and that while you'll help him any way you can, you can't get data disks out of the place in good conscience.
If you own the data, or the firm, it'll be tougher. In this case, it would likely be best to tell your friend that you must talk to a lawyer to have a contract drawn up to govern your friend's use of the data. This may scare your friend off. It sounds like he's taking advantage of the relationship.
If you have a good imagination and interpersonal presentation skills, it might not be impossible to convince your friend that the disk has been supplied with Crown 16.7 anti-copying technology, which will prevent the data from being copied accurately onto any other medium. With Crown 16.7, a file copy will be made, but digits within any numbers will be randomly scrambled, making any numerical data useless. I personally think that this is a great idea, which is why I made it up: Crown 16.7 is completely bogus, but he may not know that.
M Kinsler
clearly up too late