On Windows, the site definitions for Dreamweaver CS4 are stored in the Windows Registry at HKEY_CURRENT_USER\Software\Adobe\Common\10\Sites.
In Mac OS X, they are at Macintosh HD:<username>:Library:Application Support:Adobe:Common:10:Sites:Site Prefs.
If you have your sites running in Dreamweaver right now on an older computer you can go to the Manage Sites window and click to export the sites. Then you should be able to import them on your new computer. Also if you have CS4 on your current computer, you can de-activate it (Help->Deactivate) then install it on the new computer and make sure everything is running before you finish the process on the older computer by uninstalling.
To import/export site definitions (not site files):
On the old computer:
Site > Manage Sites
Shift click to highlight all site names
Same procedure on new computer then Import..
To all who offered to help, thank you. I moved site files and exported definitions. Based on a test of one, it works. Thanks to all. See new post on Extensions.