In case you mean the standard preview.
HKEY_CURRENT_USER\Control Panel\Desktop
and set coolswitch to 0 (or set the rows/columns displayed by changing coolswitchrows and coolswitchcolumns
One uses Alt + Escape if Alt + Tab is turned off. Tou can use Alt + Escape anytime.
From Win3.1 Resource Kit
CoolSwitch=<0-or-1>
Default: 1
Purpose: Turns fast task switching on or off. A value of 1 turns this feature on. A value of 0 turns it off.
To change: Choose the Desktop icon in the Control Panel window and select or clear the Fast "Alt+TAB" Switching check box.