Installing Lion OSX

Hi,

My brother gave me his old MacBook but he completely wiped the drive and I haven't got an operating system. The root disk says that it's locked. When I try to install Lion OSX I get a banner advising me that the app is not available, please try again later.

I have internet access but as I haven't got an operating system I can't get Safari and I can't download.

Can anybody out there help me and tell me what I need to do.

Thanks

Luke