I use Netbeans 7.0 with JDK6 under Windows 7 to design the user interface of my Java application. I apply System look and feel. But it looks the way I want in Windows but di
When it comes to window managers there is a lot more to it than just font size, for instance the width between 2 controls are handled differently in gnome & KDE. when it comes down to using the same font size across all platforms you can use Sans Serif font, this is available in all the OS'es I've worked with.
it would also be better (if you can't find serif in an OS where you want to run your app) you can download a font (free ones from GNU Free Fonts).
when it comes to setting the font sizes & the fonts, why don't you try using a theme & set the font there...
you can use the UIManager.setLookAndFeel() method to change themes.
here is a link on Look & Feel