While the Slave I is featured in Lego Star Wars: The Complete Saga on the Wii, it's not a playable ship in the game itself. It's primarily used as a transport for Boba Fett and appears in specific levels where you're required to use it to progress.
You won't be able to freely pilot the Slave I in the game, but you can control it for short segments during specific missions.
Let me know if you have any other questions about Lego Star Wars: The Complete Saga!