Probably from any P2P service. But be warned, it will probably contain a virus or Trojan. Better to just buy it from a store or eBay or something.
Blizzard offers a free download for it, if you have the CD-Key
If you already have a valid serial number you can add it to a battle.net account and download it there :)
Start>Programs>Warcraft 3 if it's not listed there re-download warcraft 3
No.
World of Warcraft expansions must be paid for to use them.
at worldofwarcraft.com you can have a 14 daily free trail
download it from http://www.greatgamesexperiment.com/download/27361
If you would like to download the official client, just go to the official website and download from the download section, its totally free.
Runescape is somewhat like world of warcraft, though it is not a complex, it is free.
You can't play dota without installing warcraft 3.
Yes
Yes. However, you can download a free-to-try trial of World of Warcraft on their website. That demo allows you to try out World of Warcraft for 10 days, totally free. If you then want to proceed playing on that account, you can choose to pay a monthly fee.