This answer record describes the necessary steps to obtain a registration code for an older version of the ISE Design Suite software, versions 3.x through 10.x.
Prior to the current FlexLM licensing scheme adopted in ISE Design Suite 11, Xilinx used registration codes to manage software release versions 3.x through 10.x.
The registration codes were either 25, 16, or 12 digit numbers.
You can access and obtain registration codes for these older ISE Design Suite versions from the Xilinx Download Center or the Xilinx Licensing Site.
Note: The next procedures assume that you have already set up a user ID and password on xilinx.com.
You will need an account to obtain registration codes.
Downloading and Obtaining a Registration Code for Older ISE Design Suite Versions
To download and obtain a registration code for an older version of the ISE Design Suite:
Obtaining a Registration ID Code Only
To obtain a registration code only, open the Xilinx ISE Registration IDs page.
Select the desired version and fill out the Registration IDs request form.
Once submitted, a pop up screen will display a registration ID and you will receive an email for your records.
See Also: License FAQ: https://www.xilinx.com/tools/faq.htm