Running Multiple Viewers
Make a new shortcut to the SL exe file.
Then in that shortcut go to properties.
Then in the properties find the Target box.
It will say something like "C:\Program Files\SecondLife\SecondLife.exe"
Just after the last " in that box put this in. -multiple
So it reads like this "C:\Program Files\SecondLife\SecondLife.exe" -multiple
That lets you open as many as your computer can handle.
(You can only have one account on at any given time of course. So you'll need a second account for the second SL client you have open. Etc. Max is 5 per household.)