|You don't remember your mother's maiden name? your first pet's name? your favorite computing.net helper?|
When setting up answers to their security questions you can ignore the questions. Just remember your answers. If they pose some stupid, irrelevent qustion just set the answer as whatever you want. If they ask 3 security questions make the answers the first 3 schools you attended or the first 3 vehicles you drove or the first 3 girls you banged (if you remember their names). That way even if someone knew you well enough to know your mother's maiden name they still wouldn't get the answer right. And if necessary you could make a cryptic note to yourself as a reminder--'q cars'--and leave it by your computer if you thought you might forget. No one seeing the note would have any idea what it was about.
Anyway, as Derek says, you need to contact whatever site is asking for them. At worst you may need to set up a new account.