Your Winstar's key has an electronic transponder chip and you can see some information here:
http://www.theaa.com/motoring_advice/security/keys.html
If you have only one key and if the chip ( or key) is broken you will have to go to the dealer with the van who will sell you a new one and will have to reprogram it. If you still have another key in good condition, you can buy a new programable key and re-programmed it with the help of your owner manual.
While a key with a defect chip will put the ignition to on ( radio and accessories etc. ) it will be unable to make the engine start.
And I would add that : for every one who has only one key, better to see if you can buy another one and program it with the old one that you have, because if you loose this sole key you will be in trouble. Dealer has to connect the computer to pull the code to reprogram a key so this could be additional $$$$$ This apply to 1999 and lat models, not sure for earlier.