I'm pretty confident you now have all the tools you need to carry on a great conversation. Most people don't realize that they are great conversationalists.
Think of how you are with your friends in a mediocre mood, think of the endless conversation you have. Now think of how nervous you get when you see a girl you're interested in. If you could take that nervousness, flip the frame to an exciting one, you can understand how great you can be.
Honestly, for me... 'hi' is usually good enough. After she says hi, you comment on something and take the conversation from there. You would be surprised how many pretty girls just want to talk. If you are wondering how to keep the conversation going, take a look at this thread:
the-art-of-conversation-vt12905.html
Just understand man, you need to get out into the real world and do this stuff to get better with it. You need to talk to girls to get better. It sucks, I know. I've been rejected more times in my life than I care to talk about. But im glad I went through that pain period. Hope this post helps.