Assuming you are using Outlook Express, if, in OE, you go to Tools, Address Book (which should then open up an Address Book window). Then in the Address Book window, go to Help, About Address Book, it will show you the location of where the address book is stored and the name of the address book (e.g. username.wab).
If you close Address Book and OE, you can then replace the (presumably) empty .wab file with the one you have on your flash drive. I suggest you rename the existing.wab rather than delete it and then copy across the one from your flash drive. If you then open up Address Book, you should see all your address info.