<p>Can I simulate in C#/C++ code <kbd>Control</kbd>+<kbd>Alt</kbd>+<kbd>Delete</kbd> sequence in Vista? 
When UAC enabled/disabled?
How it is done in XP?</p>

<p>Can you provide a code sample that works in Vista?</p>

PostMessage(HWND_BROADCAST, WM_HOTKEY, 0, MAKELONG(MOD_ALT | MOD_CONTROL, VK_DELETE));
You get PostMessage from the user32 dll
edit:
CodeProject article that has code for it
edit: There is some
discussion from VNC
on why that won't work in Vista and how to set up UAC to allow it.