Simply copy the files to the new machine and then use file/open to access
them. For Address books (pab files) you need to create an address book
service in tools/accounts. The old address book provider is still available
in Outlook 2003 and is able to open you pab files.
You're probably not using a PAB file, actually -- your contacts are probably
stored in your .PST file. Look here for all the information you need on
backup and restoration of Outlook data: