I'd buy some sites with that money, sell them for more later. If you want to start the next myspace, you will need atleast 18k.
I don't think the script is expensive, but you might need to hire someone to setup/mod. and you can spend some on marketing.. I don't know your plan, so I can't really comment on feasibility.
Spend it all on marketing. A script will be easy to come by. Or make your own, it's not hard (though you'd think so because myspace.com always has errors)
If you want to start the next big website, don't try to copy a site that is already a giant. Be creative and come up with your own revolutionary idea. Everyone already has a myspace account and there's no way you could get them to change. Unless you are creating the site for a club or a specific group or something. Then it has some value. But don't expect it to get really big unless it has something appealing about it that myspace doesn't do.