Each Addressbook is stored in the user home mailbox folder as a pair of files with the extension .PMR and .PM!. You can copy these file pairs from the mailbox folder on the old installation to the mailbox folder on the new installation.
As for the most recently used address list, it exists as a file named WINPMFUA.PM and can be copied over as well. This will require overwriting the existing file so you will need to decide whether that is what you want to do.
Whenever working with Pegasus Mail files be sure Pegasus Mail is closed.
To find out the location of the home mailbox folder use the Pegasus Mail Help menu, select About Pegasus Mail, click the Info button and look for the "home mailbox location" entry.
There is a valuable resource on Pegasus Mail filenames and extensions at: http://www.vandenbogaerde.net/pegasusmail/pf_pmfiles.html