If those do not work for you, you may need to edit /etc/gtk/gtkrc.zh_CN and change the fonts there to match the fonts you choose for programs other than gtk programs. It works for me after I made the changes for GIMP and XMMS.
For FC2, I found that it does not work (xmms and gimp). But after adding "*-medium-r-*-*-*-120-*" IN FRONT OF SimSun font in /etc/gtk/gtkrc.zh_CN(.utf-, everything shows up fine. Add the same thing in xmms' font. No need to change fonts.conf at all for this problem. See here.
http://www.linuxsir.org/bbs/showthread.php?s=&postid=640848#post640848