In Unix ~ is your Home directory. So in your case, just change the ~ to /Applications since that's where you installed WoW. Looks like the original poster has WoW installed in his home directory instead of in /Applications.

ln -fs /Applications/World\ of\ Warcraft/Data /Applications/WOW1/Data
ln -fs /Applications/World\ of\ Warcraft/Interface /Applications/WOW1/Interface

substitute the /Applications/WOW1 with the real directory of your copy(ies).

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But if you're doing that, you may as well just copy World\ of\ Warcraft.app to WoW1.app, WoW2.app, WoW3.app, WoW4.app, etc...

Here's what I initially did:

In Finder, I went to /Applications/World of Warcraft, and selected the main World of Warcraft program and selected Duplicate. I did that 5 times. Then renamed the copies to WoW1, WoW2, WoW3, WoW4, WoW5. You have to redo this step after every patch. But that's pretty easy and that's all you have to do.

Then I opened up a terminal window and did cd /Applications/World\ of\ Warcraft. In the Finder window, I opened up WoW1. I sized and positioned that window where I wanted it, then exited. Then in the terminal window, I did: cp ~/Library/Preferences/com.blizzard.World\ of\ Warcraft.prefs wow1.prefs. Then I did the same for WoW2, WoW3, WoW4, WoW5, saving each preference file to wowX.prefs (where X is the # of the WoW you just positioned.) Then I created a new shell script in my home directory called WOW-ALL.sh that does the following:

[code:1]
cd /Applications/World\ of\ Warcraft
cp wow1.prefs ~/Library/Preferences/com.blizzard.World\ of\ Warcraft.prefs
open WoW1.app
sleep 5

cp wow2.prefs ~/Library/Preferences/com.blizzard.World\ of\ Warcraft.prefs
open WoW2.app
sleep 5

cp wow3.prefs ~/Library/Preferences/com.blizzard.World\ of\ Warcraft.prefs
open WoW3.app
sleep 5

cp wow4.prefs ~/Library/Preferences/com.blizzard.World\ of\ Warcraft.prefs
open WoW4.app
sleep 5

cp wow5.prefs ~/Library/Preferences/com.blizzard.World\ of\ Warcraft.prefs
open WoW5.app
[/code:1]

Then to start up all my WoW windows, I just run that WOW-ALL.sh shell script. (Open up a terminal window and type: bash ~/WOW-ALL.sh)

This will open up all 5 windows at once and position them where you positioned them right before you did the copy from Preferences steps above.

You could even do the above preferences copy trick in combination with separate WoW directories and the "ln -fs" trick that hpavc posted. Which is pretty much how I'm running now.