X and Fluxbox :: Setting the refresh rate in X

In short, you'll probably want to use the XFree86 extension (searching around will show you that).

You can use custom modelines, changing modes on the fly, etc. but the easiest is probably editing Monitor > VertRefresh in the xconfig, or using one of those frontends (I think there's one in mydsl). See wiki for more info on editing the XF86Config-4 file.

original here.