I have Ubuntu 9.10 set up with multiple monitors. Unfortunately, the way that Ubuntu handles multiple monitors by default in 9.10 is by having a separate desktop displayed on each monitor (it is not possible to drag a window from one monitor to the other). I would like to set it up so that I can move applications from one monitor to the other. Is this possible (does 10.04 support it)?
I have this setting as default. I have two monitors and they make just one desktop. I can move windows from one to another moving then from bottom to top, and I can even manually stretch a window to use both monitors.
I used the monitor app in the preferences menu to set it up. I expect all the cards that support xrandr work the same.
So the answer is usually yes, at least with most cards.
BTW mine is an Intel.
If you have a dedicated graphics card you may find that the proprietary drivers make this easier to set up.
Most of the machines I run Ubuntu on (and all the ones with multi-monitor configurations) have nVidia cards in them. I am using nvidia's x server settings (nvidia-settings) to manage the displays. This lets me choose between having separate x servers on each screen (completely independent displays) or 'TwinView' which creates a single desktop across both displays. (this allows dragging between windows, stretching across the whole desktop, etc)
To install the proprietary drivers, you can go to System > Adminstration > Hardware Drivers (as pointed out by @themusicalduck in the comment below).
If, however, you want the latest drivers (which typically offer bugfixes and performance improvements) and don't mind the hassle, you can go here for nvidia or here for ati. Put your card's model in there, choose 32bit / 64bit for your setup and download.
ps. I don't know about the ATI driver, but but the nvidia driver comes as a script to run that will install the driver automatically, compiling the kernel modules as required etc. However, you need to shut down the display before you can update its drivers, which can be scary. Just follow the steps in this guide and it should be fine! ('Logging in as root' means typing sudo su (or prepending sudo to all subsequent commands)