This is generally a browser issue. Explorer & Netscape don't handle dmg files very well. So poorly in fact that you probably have an incomplete dmg. If you re-downld it using Safari then the file will be a little larger in size & should mount without problems. If need be, drag & drop the dmg onto Disk Copy to mount it (not double-click it.) To find Disk Copy, go to menu bar & select Go>Utilities & you'll find it in there.
Sounds like a scam version! As Only A Hobo suggested, only get LW from the "official" LW site: http://www.limewire.com/english/content/download.shtml