How can I import my address book from M. Outlook (my desktop) to Windows Live Mail (my laptop)?

This will tell you how to find the address book on your XP computer.

http://www.brighthub.com/computing/windows-platform/articles/65368.aspx

Copy the file and move to the new computer.

Then use the steps here to import into Live Mail

http://email.about.com/od/livemaildesktoptips/qt/Import_Outlook_Express_Address_Book_into_Windows_Live_Mail.htm

To recap...
copy .wab file from old computer.
Select File | Import | Windows address book (.WAB) from the menu in Windows Live Mail. (direct it to the place you put the .wab file.)

Another easy way is to create an export file in Outlook by going to FILE -> OPTIONS -> ADVANCED (might vary depending on the version of Outlook). This creates a comma separated value file (*.csv) that you can copy over to your other computer then import.