Is it possible to start a game with characters from an old wiz8 game. I didn't finish yet so I'm asking if you can import your old party like in Baldur's Gate.

No, once you complete the game your characters are saved in a special end game save. But you cannot use that to import or start a new game. About the best way to import characters is using a Wiz 7 characters.

Knarfling

I don't have wiz7 so it will be hard for me to import them. Since there will be no wiz9 the special saved end game will have not much of a use!

Yes, you can use "Simple Editor for Wizardry 8"
Filename w8edit.zip
Size 93.6KB
URL http://www.wizardryrealms.com/wiz8/cheats.shtml

Backup your SAV file and CHR files first(when you export
characters I don't think it will overwrite them, just adds
a 1 to the end). But be safe.
Unzip, run editor, load your SAV file. Then export all
of your characters. Then start a new game and add your
old characters. Your gold does not follow to new game.