You Must go to Battlenet.com and select "Classic" Games. If you do not have a Battlenet acount, you must create one.
Start>Programs>Warcraft 3 if it's not listed there re-download warcraft 3
You can't play dota without installing warcraft 3.
Yes
If you already have a valid serial number you can add it to a battle.net account and download it there :)
No, World of Warcraft is not on Steam. If you want to download it, got the the official World of Warcraft site to download it.
Blizzard offers a free download for it, if you have the CD-Key
It's a mod you need to download it from the hivewrkshop
Warcraft 4 does not exist....yet
Log-in to your account management on the warcraft site and scroll to the bottom where it says download client, their is then a link for PC & MAC :)
If you do not have the install disc for World of Warcraft, then yes, you have to download it and let it update to the current version.
If you are looking for a Warcraft 3 The Frozen Throne delay reducer here it is download it at http://files.filefront.com/W3DR+1600rar/;12134088;/fileinfo.html Thank you :D
Go to www.blizzard.com, and look for software updates.