There's a sticky in the general forums about this:

http://www.dual-boxing.com/showthread.php?t=19768

From the part about Eve Online:

You are welcome to use multiple accounts at the same time, no matter how many accounts you are using.

What we understood you were asking with regards to multiboxing, was controlling all of those account with a single keystroke program or mouse click copy program.

To make it more clear: You may use as many accounts as you wish at the same time, however you may not use a program to control more then 1 account at the same time with the same keystrokes/mouse, you will need to actually switch between the windows to control them.