Has your XF86Config file been setup for 1024x768??
See the cut out section of my XF86Config file as an example below:-
Device "NVIDIA GeForce 2 MX (generic)"
Modes "1280x1024" "1024x768" "800x600" "640x480"
Using the above example, you should be able to use the CTRL-ALT-+/- (Numeric keys) to switch between these modes.
These have worked well for ALL the installs that I have done.. If it doesn't work, then there may be other issues causing some problems.
Possibly the Horizontal and Vertical information in that same file maybe not allowing you to go to 1024x768??
You will need to check the Toshiba Site to get these values that are required by X, to set the screen to the desired resolution.