here is the answer from Xilinx:
5.1i/5.2i Modular Design - How do I enable the Modular Design flow in the 5.1i/5.2i software release?
Family: Software
Product Line: Other
Part: Modular Design
Version: 3.1is3 Record Number: 12260
Last Modified: 03/27/03 15:56:18
Status: Active
Problem Description:
Keywords: 5.1i, 5.2i, modular, design, feature, flow, install
Urgency: Standard
General Description:
How do I enable the modular design flow in the 5.1i/5.2i software release?
Solution 1:
In the 5.1i software and all previous versions of the software, modular design was a separate tool that you had to purchase. After purchasing this tool, you then downloaded a zip or tar file to install it. These install files are no longer available on the web.
In the 5.2i software, modular design is part of the standard software package, and it is automatically enabled. If you do not have access to modular design and would like to use it, please upgrade to the 5.2i software.