Under "Screen resolution" in Ubuntu, I don't have my screen's native resolution (SyncMaster 226BW).
What's the right way to make Ubuntu detect it?
If it is not detecting the right resolution it may be that you need to install the drivers for your display device, if possible. This is most often an issue when using DVI monitors. Your also going to want to make sure your graphics card drivers are up to date as well.
If you have an Nvidia graphics card there's a great tutorial here on getting the right drivers installed in Ubuntu.