How can I manage to connect 5 monitors to one PC?

"The rigs that I have seen with many monitors were all done in one of two ways:

They crammed as many PCI(-E) video cards into a PC as possible.
They have multiple machines powering the different displays. This one is pretty popular with the flight-sim guys. Three big monitors for the cockpit front windows, and then many smaller screens for the different flight instruments. Seems to work well."

Matrox offer cards that support up to 4 monitors. Presumably you could have two cards in a machine.

"In addition to your PCI Express card, you could put in some regular PCI graphics cards (yes they still make 'em). Depending on what you're doing there may be some performance issues.

You may also look for stores that target the niche groups that really have a need for more than 4 monitors and see if they have some special hardware."

I've used the VGA Y-Cable Splitter (also available in DVI) to have multiple Monitors on one VGA (or DVI) Port.