[davidlumley]

To be clear: taxes are due when you receive the shares. For options, that's when you execute/purchase your options not when they vest.

edit: (in the US at least)

[johnebgd]

The taxes can also be due when you receive your options. That can depend on if you purchase your options or if they are granted to you and entitle you to a discount.

YMMV but an NQSO purchase agreement can be your friend.