each screen mode has it`s own settings for position on the screen, brightness etc (at least on my machines they do), you have maybe never used the lo-res 640x480 setting before (the DB default mode IIRC), so the system has no memory of where the screen should be for that mode, just adjust the position on your monitor with the settings controls on the front and the next time you run that mode windows will remember and set it back to that position, it won`t hurt the position of your windows screen since that will be at another resolution with it`s own settings, (or just set the screenmode to the same as your desktop so it uses those settings) cheers.
Mentor.
System spec : Pentium 3.0Ghz, 512MB DDR, 2x160Gb HD (using icewave hd coolers ), DVD RW/CD RW (all modes), multimedia front panel, 6 way surround sound, ATI radeon 9800Pro 128mb.