Sitting in the front lawn of the home he moved into a mere two weeks ago, Marteniz Brown calmly tells his life story. It's a tale he's told time and time again over the past 10 years.

"When I was 17 years old, I didn't really have a clear direction about what I wanted to do or where I wanted to go to school," the now-27-year-old starts. "So I thought about it and sat around and took some time to talk to my mom about it, and we came upon the military."

The military was the perfect choice for this young man from Detroit. He'd have the opportunity to see the world; perhaps he'd even get stationed in Japan, which was always a dream.

So Marteniz met with Air Force recruiters and got the ball rolling. He took his Armed Services Vocational Aptitude Battery (ASVAB) test, completed a physical -- even signed the paperwork. The next few years of his life were settled; Marteniz was an Air Force man.

But then, with boot camp looming just around the corner, his phone rang.

"Two weeks before I was supposed to go, I found out some information that, you know, changed my life," he says. "And that's when I found out I was HIV positive."

Marteniz hadn't even realized the blood drawn at his physical was tested for HIV. In fact, when the Air Force official called to tell him there was a problem, but refused to be more specific over the phone, Marteniz assumed his ASVAB test score was too low. It never crossed his mind that he was HIV positive.

"It crushed me because I knew I couldn't serve my country, and it chopped a lot of options out of my life," Marteniz says. "I knew that my mom had worked her whole life to try to take care of me and my brother, so it's, like, my turn. It's up to me to take care of [them]. So I felt like I was a disappointment when I found out that information. I really felt like a loser."

The dream of serving in Japan would never be a reality. Instead, Marteniz, just barely 18, was tasked with figuring out how he contracted the HIV virus. He promised his mother he would talk to all of his sexual partners, a promise that turned out to be easy to keep: There had only been two.

The first was Marteniz's only romantic partner, a young man he had met in high school.

"We had some ups and downs, some breakups," he says of the first boyfriend. "It was a new world to me, you know. I totally was really naive."

And during one of those "breakups," Marteniz became sexually active with a second person. They did not use a condom.

"I knew the consequences of having sex, but I didn't think that, because of who I was with, that it would be an issue," he states. "I thought it was OK because that person was young, clean-cut image, attractive. There was just no way this person could have HIV."

He was wrong.

"I put my trust into someone, and this is the result of it. I cant really blame them because I had a choice in the whole thing, to use a condom or not use, you know, so there's not blame. I just made a choice. I trusted someone, and this is what happened."

By the time Marteniz found out about his status, he and his first boyfriend had reconciled. They remained together for the next seven years. But with the military out of the picture, he had to figure out what to do with the rest of his life. He turned to education.

"Especially being someone who is HIV positive, I felt like [teaching] was my duty," he says. "God must have placed this on me because I can handle it, and I can educate people about it."

He began accepting speaking engagements and even appeared on TV. In 2005, he played an HIV-testing counselor on the UPN sitcom "Eve."

But it was the safe-sex presentations at schools that Marteniz found the most trying. Often school officials forbade Marteniz and his fellow safe-sex presenters from using the word "condom" -- tricky for a presentation about HIV.

"It was really hard to actually just think about what [school officials] were asking us to do and how it contradicted itself," he says. " 'Well, you can talk about sex, but you can't say condom. You can talk about HIV, but you can't say condom.' " Officials, instead, preferred the more generic phrase "Protect yourself."

These limitations encouraged Marteniz to become one of the thousands of people who have uploaded his or her personal video blogs -- or vlogs -- to It's Your (Sex) Life, the new social-networking site created by MTV's Think campaign.

It's an issue that is particularly relevant this weekend: World AIDS Day is Saturday. So while most people are checking their social-networking sites for crazy frat-party photos or trying to find a date for tomorrow night, ItsYourSexLife.com showcases people telling their personal stories about living in the time of HIV and AIDS.

For Marteniz, vlogging opens more doors. "The big thing is that you can reach more people, especially people who may not exactly feel like they can actually come out and ask this stuff to their parents."

Marteniz hopes that everyone who sees his vlog will know that he's well and happy. His T-cell count remains high; he's even gone off his meds. He's dating. But he also hopes people will listen to his life story and take it to heart.

"Maybe they can get online and see something, see me talking, and they can relate to what I've been through," he says. " 'If he can get it, then I can get it.' So once they start putting two and two together, they will make better choices. And I think that's what will happen. And I will feel better if I reach just one person."