Uhh... you really can't do much to upgrade your PowerBook. You're not going to fit a video card in there, because everything is packed together and much of it is integrated.
You should return the video card unopened if possible. The best you can really hope for is putting in a bigger hard disk drive (storage space) or increasing the system RAM if it is not at max (that's the fast memory that is used by the computer for temporarily storing running programs, games, the OS, etc).
If your system RAM is already maxed out, you have little upgrade options, honestly. The PowerBook is not a gaming system by any means.