Installing Linux As A Virtual Machine On Mac

[Jane Jordan (gmail)]

Is there a free program to install Linux on the iBook as a virtual  
machine?  I guess what I've been told is that I can run it at the  
same time I run the regular OS and just kind of command-tab between,  
as though they are windows.  Is this possible?

If so, what is the program called, where can I get it, and what is  
the cost?

Thanks for your assistance.

Jane