You need to have a save created during the Ice Plains or Order of the Flaming Rose Cloister portions of the Epilogue. The Witcher 2 recognizes only saves made before the last fight.
The save should be located under:
and the game save files should have a name like the following:
xxxxxx - Order of the Flaming Rose-xxx.TheWitcherSave
where xxxxxx is a serial number for the save.
Then, in TW2, select "New Game" then "Import Witcher 1 Save" from the main menu to import TW1 save.
Further info and files path for PC can be found here.