WDs tend to be very good about documenting thier jumper positions on the actual drive. on the top of the drive usually at the bottom of the sticker there should be a little diagram showing at least 2 different jumper positions (there may be as many as 6) there should be a listing for slave, there maybe a second listing for slave, but if you read everything you should be able to see one is for special applications and the other is standard, usually the one jumper solution vs two. On the front of the drive where you plug in the ide cable there should be a set of jumper terminals that look like the diagram. Place a jumper as they show and everything should be wonderful. Usually the there will be 6 terminals and the jumper will go on the middle two for slave but the drive will tell for sure.
Only one problem... did jumper just loose contact and its still on the drive or did it fall off... any jumper will work if you can find one, but you may have to scrounge an unused on from your motherboard or sound card or modem. the Quantum may even have a spare. As long as the jumper only hooks onto one terminal and not 2, its a spare.
without knowing your model # I can't pull up specifics, but
here is a link to a picture of what I am talking about... just have to scroll down a little.