XFCE is nice, but it lacks a number of handy Gnome features from what I've been able to tell. It's so stripped down that it feels like a toy gui, lacking in a number of solid tools. It doesn't have, for example, any method of even changing screen resolution or refresh rate--traditionally a rather weak point with Linux guis, but one which is important in my opinion since 1280x1024 at 60 Hz is horrible, and I don't want to have to mess about in XFree86.conf just to change something like that.
"traditionally weak" is an understatement. Until recently, there was no way at all of doing this within the GUI. Have you tried running 'gnome-display-properties' under xfce? This is the gnome applet which makes use of the xrandr extension to set your screen resolution. The fact that you're not running 'Gnome' (and metacity) shouldn't matter.