Adding additional Monitors to a MacBook

I have a MacBook that is 4 years old. I do not want to upgrade to a newer model, it's working great. I have attached one extra monitor via the laptop's Mini DVI, using a Mini DVI to VGA adaptor. I would like more screens, up to 4 or 5 including my laptop screen. How can I add two or three more monitors? I have read online articles regarding USB powered adaptors, with powered routers. Any suggestions would be appreciated. BTW, I'm running Mac OS X Version 10.7.5 . In advance, Thanks! Schmidt29642