First let me say congratulations, and I mean that, I think in time you will see this as a good thing, even though right now such a thought seems impossible.
Now, why is she telling you? Since it's been 7 years already I doubt it's about money, perhaps she has felt guilty for not letting you know, perhaps she's wanted to tell you all this time but never been able to bring herself to do so.
Maybe she just wants you to know, in case you want to do something, and if you don't she'll be ok.
Or maybe she wants you involved, even just at a small level, maybe she just wants you to meet the kid, or hang out with him/her from time to time.
There's just so many possibilities at the moment, but I know this is not a situation that can be handled drunk.
As far as telling your parents and girlfriend is concerned, I don't think you need to worry so much. Sure it'll be hard bringing it up, but it's not like you're going to be judged greatly for it (surely?), and I think your parents at least will probably be happy to hear they have a grandchild.
The girlfriend is a trickier one, because she might become jealous, or concerned about the relationship. She might get concerned if you don't want to hang out with the kid, too.
Step one is to find out what the mother wants, and try and deal with it calmly. Then there's the next big question: what do YOU want?
Don't worry about money, or judgement from friends and family, forget all that crap and think: you have a kid, do you want to meet him/her? get to know them? pretend they don't exist? Help them? Not help them?
She has given you this information and it seems like the ball is in your court now, so take some time and think about just how you feel.
You can't judge a book by it's file size