To learn more about a classmate or random hottie, college and high-school students no longer need to rely on student guidebooks or yearbooks. Heck, you don't even have to talk to anyone.

With Web sites, some of which date to the late 1990s, students by the millions are creating online profiles with photos, contact info, descriptions of their likes and dislikes, and a list of friends who'll vouch for them.

Some sites are thinly veiled online dating sites; others are used as message boards, to stay in touch with friends, form study groups, sell textbooks, gossip and download music and games.

"I think its attraction — and that it's so widely used — is that it's something fun and like an encyclopedia of your friends," said Chris Hughes, a junior history and literature major at Harvard University and co-founder of thefacebook.com. Many sites provide privacy features that allow users to make their information accessible only to specific friends or certain schools, dorms and regions. There are also options to block other members from making contact. A general rule: Only provide as much information as you're comfortable with.

"People of our generation are pretty savvy and realize anything they put on the Internet can be seen by a lot of people," Hughes said.

In addition to the Facebook (see accompanying story), here are some other popular networking sites, according to local teens and twenty-somethings, and recent figures from comScore Networks, an Internet research company.

CampusNetwork.com: Big among Ivy League schools, this site, a predecessor of the Facebook, includes student pictures, biographical information, blogs, photo albums, online radio stations and postings for upcoming parties and events. Must have a university domain name to participate.

Friendster.com: Somewhat similar to online dating. Members create profiles, list their friends and use the site to meet new people through the "friend-of-a-friend" approach. Losing steam since debuting in 2002, according to comScore Network, which points to a decline in site visitors. Likely to be used more by twentysomethings than teens.

Myspace.com: Don't be surprised to see some racy photos among profiles here. Along with trying to find a match for your friend or yourself, there are other features, such as downloading music and games (including the old-school Asteroid), album reviews and discussions about everything from drag racing to how to tell if you're in love. Members can also instant message and vote on whether other members are hot or not. Judging from profiles, appears to be most popular with high-schoolers and undergrads.

Tickle.com: In addition to online matchmaking, there are polls, personality tests and astrology readings. A bit tamer than other popular sites.