What do you mean when you say "i got two vga connectors but tower have one vga connector" I don't understand? You have 2 vga connectors where?
Many if not most newer graphics cards have two outputs and you can connect a screen to each of them if thats what you want to do. If the tower only has one graphics output then yes you need to buy another graphics card that will output to 2 monitors. Depending on what you wish to use it for it doesn't have to be an expensive card.
I currently run 2 monitors from one tower, the link that anskeyber is what i followed to do it.
I don't know what the cheapest card with the dual outputs is, I'm sure another forum member can help there. I'm using a nVidia 6600Gt and it can play movies across 2 17" TFT screens quite happily, but not games.
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