There is not much I can offer here except you check the manual. I can't since you omitted the required details.
About it being a pain. Microsoft didn't make this the easiest OS ever. Pain or not, they expected us to deal with it.
I have a laptop running XP, and an extra monitor.
I can't extend my desktop to two monitors. Both monitors appear in display properties/settings, but when I click the 'extend display' all I get is both screens displaying the same thing (e.g. mirror).
The really infuriating thing is that I have had it working fine before, but whenever I used to go back to just using one monitor, all the settings changed, and changing it back was a pain.
The issue is clearly not to do with drivers because I have had it working properly before, including last week. I have changed nothing since.
It was always a bit funny though and took a bit of restarting and all that to change. But this time even that didn't work.
The problem seems to be in XP. Anyone know a fix?