ANYTHING on the internet can be accessed by anyone with a little computer savvy. Once it's there, it can never be completely erased.
One of the application questions for the school system where I work is "Do you have a social networking page?" They are allowed to ask. If you say "yes", they are allowed to look. If you say "no" and are lying, you won't get hired. Most employers do a FB and MySpace search before making an offer of employment.
Just because you have everything set to "private" doesn't mean that the folks posting pictures OF YOU have the same filters. If I were you, I would go through any pictures where you are "tagged". If you don't like the picture, "untag" yourself. The original poster won't be allowed to re-tag you.
A college friend of mine posted a ton of old sorority pictures of us to FB long before I had an account. She tagged me in them... I "untagged" myself in many of them. While I loved my Tridelta days, I don't really need a ton of pictures of myself in "jungle wear" or at a "naughty school girls and dirty old men" party and I certainly don't need my colleagues seeing them!