XP guest video resolution and dual screens

Mepis Linux 6.5 host (basically Ubuntu 6.10) and XP Home guest:

I'm using Linux on two widescreen 19" LCD monitors (nVidia grapics chip and drivers) running at 1440x900. I prefer running Parallels in windowed mode so I can easily turn off USB devices (printer) for XP.

Everything works great in single monitor mode. I get a nice 1280x768 option in XP that sizes just right for my needs.

However, in dual monitor mode I only get 1042x768 and 1280x1024 as the closest options.

So what determines what resolution modes XP sees from the Parallels adapter and can I change this? Full-screen mode is not an option as it stretches the XP window across both screens.

Thanks,
kumar