Is it at all possible to switch between Windows and Ubuntu by press of a button, on a system with Windows 7 - Ubuntu 11.10 dual boot set up?
You cannot have two operating systems running next to each other at the same time. So there is no way to simply press a button and go to Windows.
What you could do is use virtualization, for example using VirtualBox. You boot one operating system normally, and run the other operating system in a virtual machine inside VirtualBox.
Note that there are some limitations to this - the OS running in the virtual machine does not have direct access to the hardware, so performance might be a little lower and 3D graphics etc. won't work as well as when running natively.
When you are booted up in Windows or Ubuntu, you can't switch to the other one. In dual boot you can be either in one or the other. If you want to switch between them live, you want to decide on one of them being the host and then through a virtual machine (WMPlayer) add the second OS.
This will have a master/slave, host/guest relationship between the 2 OSes. But one of them will be virtual.
It's a good way to test one of them.
The only way to boot a Windows install of any kind after booting into Ubuntu is by running it within a virtual system. You can create a shortcut link placed on your desktop that will autorun virtualbox for example, thus giving you the effect of "pushing a button" to run Windows. It's an option inside virtualbox to create this shortcut too, so it's fairly simple.
Actually, provided your hardware is compatible, you could pretty much accomplish what you have in mind using XenClinet 2 under which ALL of your operating systems would be running as virtual operating systems.
Note that, at the very least, your CPU must support VT-x or AMD-V to run XenClinet 2. Also, XenClinet 2 is currently in a "free to try" phase of development. Not sure what will be the cost/availability of XenClinet 2 in the future.
Of course you can have two(or more) Operating Systems running at the same time. That's no problem.
So switching between both with a key combo is very much possible (and likely).
(Switching between Ubuntu and Windows 7 is fully supported by the time I write this.)