the newest driver for 4800 series cards doesn't keep extended desktop mode after reboot.
at least not on my computer,
I have a 24" samsung and a 22" Philips, i use the samsung as my primary, after installing the driver and restarting, the philips was the main monitor and it wasnt extended
thinking it was just new install problems, i reset everything back the way i had it, closed all windows, and reset my computer, only to find it ws back on single display on the philips, i tried this several times with no success until I rolled back the driver.
after rolling back the driver, the display settings were rolled back as well, suddenly the primary display was on the samsung, the extended was active on the philips, and i didnt even have to set anything.
i found that was quite interesting, meaning it quite isolate the new driver as the culprit of not only the wrong settings, but in actually forcing those settings on my displays