Well yes it's not easy to do it seems.

In Windurs all you do is plug another graphics card into the
motherboard and hook it up to anonther monitor and hey presto you have
dual display. In fact you can put in as many as you have slots for on
your motherboard. You don't need any fancy cards or drivers it just
works. Its been like that since win98.

So I thought this would be the same with Ubuntu. I've got a variety of
old cards which work and tried it. No luck :o(

I've even got it now with two identical PCI cards and the same monitor
to each output and the best I've seen is a tiny white spot on the top
right hand side of the other monitor. So I guess something has
happened but it's not really working :o(