virtualbox.org

I am using Ubuntu as parent and Windows XP SP3 as guest. I am having 3 Virtual Boxes in one parent machine and need to keep all active at a time. So, need to keep VBs with optimum resolution. However sometimes we need to maximize it manually. I want to automate to change the virtual box to maximize or full screen with code or any command.
Is there any system command or any third party tool or any thing which resolve my purpose. (Except Host+H or commands through Machine menu).

Thanks in advance.

That's really a question about the host software, not VirtualBox. If you can send a message to the host window to maximize itself then the guest should be able to cope with that in the normal way. If by maximized you mean fullscreen mode then I don't immediately see a way to set fullscreen mode programatically, except perhaps by injecting keystrokes into the VM process, again on the host. I don't know of a way to select fullscreen mode from inside the guest. The guest can force a particular display size (less than the maximum), but whether the VM window is framed or not is a matter for the host software, which the guest doesn't control.