HPV is tricky to describe without going into too much detail.
There are quite a few strains - think of it like a cold virus - there are a lot of them out there! However, there are a couple of strains that are potentially harmful - essentially able to lead to cancerous growth in that area of the body, which can lead to cervical cancer. However, if your girlfriend has been 'fine' since she was 17, and has been getting checked annually, I would not be too concerned.
I would be most concerned about her health - ensuring that she is getting her PAPs regularly, and letting her health care provider know that she had a positive HPV test when she was 17, if she sees different health care providers for each PAP.
For males, it is a bit trickier. It can cause cancer (depending on the strain), but its much more rare in males, than cervical cancer is in women. I'm not even sure what part of the body it can cause cancer in in males, but somewhere down there! However, if your girlfriend doesn't have any symptoms and hasn't had any positive tests, I think you'll be fine. HPV is fairly common and many young people have it by now, just based on the sexual promiscuity that occurs in our society.
There is the Gardisil vaccine, which males can have. If you are really concerned about contracting the two most high risk strains of HPV, you can get it, but it is expensive. Its also kind of moot if you have been sexually active already, and is mostly recommended for those who haven't had sex yet.
Bottom line: its a fairly common virus that many young people have these days - and is only a concern when the cells become cancerous in the cervix area - so as long as your girlfriend stays on top of her PAPs, you and your future family should be good to go :)