Can I run two WoW accounts on one (not at the same time) computer? Would I have to install both game CD sets? I was thinking I could just change the sign in name and password between each account! Does that make sense or not possible?
Yeah, the number of accounts you have doesn't make a difference. You can have as many as you want as long as you have upgraded each account with a Burning Crusade key so you'd have to buy TBC individually for each account. You can play multiple accounts at once on networked systems or on the same machine if yours can handle it.
The only thing that matters is that the accounts are active on the Blizzard site and have been upgraded for the Burning Crusade. =) Other than that you can play any account on any machine that has Warcraft installed.
Yes, each account needs its own cd-key to go along with it. Whether they are played on the same computer or not (at the same time or not) is up to you.