Whenever you install any program on a mac (OSX), you'll need an admin password. That's natural. So if you don't have admin rights to your comp., you'll need someone who has those rights.

If that's not what you mean, then did you get LW from here: http://www.limewire.com/english/content/download.shtml

If you got it from anywhere else then it's probably a scam version. Who knows what could be inside it including spyware, diallers, etc.

BTW instead of double-clicking the dmg, drag & drop it onto Disk Copy. Have you repaired permissions on your comp. SAFE Boot & Repair Permissions and Resolving Disk, Permission, and Cache Corruption