Typically for founders and employees you assign options that vest (an option to buy a common share at a given price).

The basics of venture math is described by Brad Feld:

* http://www.feld.com/wp/archives/2004/07/venture-capital-deal-algebra.html

The preferences that an investor can put in deal structures change. See http://www.feld.com/wp/archives/2004/07/liquidation-preferences.html

You should talk to a lawyer that has experience with share holder agreements, employee stock option plans and the tax implications of the different decisions based on your jurisdiction.