I want to set my editor's font as Monaco-11, but it has no anti-aliasing effect. And when I set it to Monaco-12, anti-aliasing effect works. How can I make it also work for Monaco-11? I'm using Ubuntu 9.10
I suspect that anti-aliasing is deliberately disabled for small font sizes. This is often done because at small sizes anti-aliasing makes fonts unreadably blurry.
You can probably configure this behaviour. I believe on Ubuntu this is controlled via Fontconfig. Fontconfig has configuration files in the standard places (/etc/fonts, and ~/.fonts.conf). See the user manual for details.
You probably want to add
edit commands to enable anti-aliasing. See e.g. this blog entry. You may have to experiment a bit...
Also see this related question.