MySpace girls that are physically attractive (6+) are 50% attention vvhore teenagers that are just looking for praise and adulation, 25% single mothers desperate to find someone who will put up with their encumberances, 20% men posturing with women's pics because the like screwing with guys on there, and 5% normal girls that have no huge problems/baggage and are there to meet people for normal, healthy relationships/friendships.
Not impossible, but the odds are stacked against you from the start.
And not to crash your hopes, but any internet "hi" message is virtually worthless. Girls can and usually will act with more aplomb and openness on the internet because of it's inherent anonymity. They can lead you on and drop you when they feel like it because they don't know you, don't have to look you in the face, and don't have to worry about you stalking them or goin gto their house if they piss you off.
As far as sarging them, start one convo about something that they've talked about on their main page, then after their response tell them that you'd really like to talk to them more about it but you're not usually on the computer enough and get a phone number.
MySpace/HotOrNot/Match.com/PlentyOfFish, all of those places can be ok for finding people that you might not otherwise ever see, but you're not going to build anything substantial on the internet. Now that you have an open lin of communication, get the number. If you don't get it in three messages, move on. If you get an AIM or Yahoo Messenger, then give it two convos on there to get a number and if you don't get it by then, bail. If you don't have it by then, either you're not getting it at all, or she's going to make you jump through hoops to get it. Screw that.