When installing Microsoft Beta and Release Candidate software it is always a good idea to read the Knowledge Base article and not just the download details.
From the Knowledge Base Article:
"The Service Pack 2 is time-limited software. You must uninstall this service pack software before you install the final version of the service pack. Also, this software will no longer operate after May 1, 2010, and you must uninstall this software before that date.
If you install the Service Pack 2 , we strongly recommend that you also install the final version of the service pack when it is released. To do this, you will be required to uninstall this prerelease software.
Notes
* After you install Service Pack 2 , your desktop may display the following text:
Evaluation Copy
This text does not mean that your system is no longer ?Genuine." This text only indicates that you installed a test version of software that is time limited.
* The Evaluation Copy text may be displayed on the second startup after you install the service pack. Also, the Evaluation Copy text may remain during the first restart after you uninstall the service pack. However, this text does not appear after the next restart."
Note 2 key things in the text above:
1. THIS IS TIME LIMITED SOFTWARE AND WILL STOP WORKING ON MAY 1ST 2010.
2. YOU MUST UNINSTALL THIS VERSION BEFORE INSTALLING THE FINAL RELEASED SOFTWARE.
Worst case, you may need to use the restore disk or partition to repair your computer. Make sure that you have all of your data and critical information like network settings and product keys backed up before you perform a system restore.
Chas