You should have received a form from your employer at the time you purchased the stock. This form 3922 is necessary to provide you with information to determine your gain or loss and how much is possible ordinary income and how much is capital gain or loss.
If you don't have this, then you need to obtain this information from your previous employer. The company should also have a stock plan administration web site to provide assistance.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
