external monitor with 12" G4 aluminium powerbook?

["Clea F. Rees" <reescf@gmail.com>]

I was wondering if anybody had managed to use an external monitor with one of the 12" aluminium powerbooks. These have a 1.5 GHz G4 processor and a nvidia graphics card. Output to an external monitor is via the mini-dvi port. In my case, I'm trying to use this together with the mini-dvi to vga adaptor which came with the laptop. 

My (meagre) understanding is that xfce offers good support for xinerama etc. and the display preferences in the settings manager do recognise the external display as connected. In fact, the display is listed not once, but twice - once as an external monitor and once as TV. However, I can get nothing but a blank screen.

The same monitor works OK using the same adaptor under OS X, so I don't think it is the adaptor etc. (At least, I'm having problems with OS X but it usually works OK.)

I usually use the external output for two things - to connect to a larger monitor when in my office (which has the added benefit of not having the vertical column of always-on pixels my laptop's screen now boasts) and to output for LCD projection when teaching or presenting papers. In both cases, I use the mini-dvi to vga adaptor. 

I'm running (almost entirely) wheezy/testing and using the nouveau drivers. Probably unrelated but I also don't have control of the backlight under Linux.

Any advice?

Thanks,
cfr