I've Just recieved the following email from Microsoft explaining some changes so I thought I'd share it with you lot in case you experience any issues ;

To avoid potential business disruptions and maintain the highest level of satisfaction with Windows Vista deployments, the most important activation changes for you to be aware of and to inform your customers about are:

1. Activation: In the first 30 days of use, all new installations of Windows Vista must be activated by the OEM, through Windows Vista volume licensing technologies, or by the end customer. If Windows Vista is not activated in the first 30 days, the system will operate in a reduced functionality mode.

2. Validation: In order to protect users from being victimized by counterfeit software, and to protect Microsoft’s intellectual property, Windows Vista includes ongoing validation. Through validation, if non-genuine Windows Vista is detected (including non-genuine product keys, cracked or tampered code) the system enters a 30-day grace period. During this time Windows Aero and ReadyBoost features are disabled, and Windows Defender and Windows Update will have limited capabilities (optional updates will not be available through Windows Update, and Windows Defender will only remove critical and severe threats). In addition, during this grace period, a message will appear repeatedly, encouraging the user to take the steps necessary to activate with a genuine product key in order to regain the full value of Windows Vista and to prevent the system from going into a reduced functionality mode.

3. Reduced Functionality: After the repeated prompts above, and if Windows Vista is not activated in the 30-day grace period, the system will operate in a reduced functionality state until a genuine product key is used for activation. In this reduced state, the user will have access to their files and applications, and access to the Internet. However, the desktop will be simplified with only a browser (no Start Menu or Task Bar) and Windows Vista usage will be limited to one hour sessions, at which time the user is forced to log off. Additionally, users may boot the system in Safe Mode in order to access or back-up personal data and applications.

I hope this information helps