I want to have my system with me in another city. I know that it strongly depends of my chipset. I have P35 (Gigabyte P35DS3R). Another machine also Intel-based but chipset is G31 (MSI G31TM-P35). Is it possible that my system will start on that machine when I plug in my hdd?
Windows 7 will be aware that the hardware has changed and will ask you to call an automated 1-800 number to verify and re-activate your Windows installation and again on your return when you plug your HDD back into your current system.
Microsoft can and will limit your number of activations, eventually making it more and more difficult to re-activate. I wouldn't recommend switching on a regular basis.