I was in a similar position when I wanted to start multiboxing. I didn't want to actually go out and buy the games at retail price from a local retail store, so I search online and purchased CD Keys, both for WoW and BC. I'm not saying I wanted to steal them or anything, I just figured I could probably get them cheaper from somewhere online, and I actually ended up saving a lot more money. I also do the same when purchasing 60-day prepaid game cards for each account, and again, I save a lot more money that way.

So, I have purchased my original copy and had it installed, then I just copied the World of Warcraft folder 3 more times and activated new accounts by using new CD Keys which were legit. No sense in wasting instillation CD's.



EDIT: I want to clarify why I chose to buy CD Keys online. I used to play World of Warcraft when it came out, but then stopped when I hit 60 and then Burning Crusade came out. BC was $40 when it came out, and WoW was $20.00 - so, I went to Walmart and bought both when I found out my younger brother started playing again. I get the games home, and nothing but their manuals were in there. So, I had wasted over $60.00. When I went back to Walmart, they couldn't do anything for me, and refused to give me new copies, and refused to give me my money back. I ended up attempting to play again months later after playing Guild Wars (and disliking it), when Amazon.com was having a sale on WoW Battlechests.