it should take whole screen

Huh?! 800x600 is NOT the whole screen of a native 1280x1024 monitor. This is due to the monitors' auto-adjusting feature whereby it makes the game environment the computers' screen size and resolution. My previous LCD (18.1") did not have that feature and ran the game in its own native resolution/screen size relative to the monitors' inherent resolution.

When you have a normal monitor, then full screen is always really full screen (even if it is 640*480 on 1600*1200).
But LCDs had sometimes problems with non-native resolution (so therefore it probably behaved as you described with your older LCD). That was non-standard behaviour (even though you liked it).

Mirek

You can try to fiddle with these setings in the config file:

fullscreen=false
fulldouble=true
fullfixed=true
fullresolution=1024x768
output=ddraw
hwscale=1.00

Fullfixed did the trick...unfortunately, it doesn't work with opengl as the renderer, but that's ok. Thanks for your help.