my freind told me that to unlock some characters in mario kart wii is to do time trials. i did some but nothing happend. does any one know?

You have to play a certain number of courses, or unlock a certain amount of Expert Staff Ghosts(beat the regular ghost by ~5-10 seconds).

Gotten from GameFAQs:

Baby Luigi - Unlock 8 Expert Staff Ghost Data in Time Trials
Birdo - Play Time Trials on 16 different courses or win 250 Wi-Fi matches.
Funky Kong - Unlock 4 Expert Staff Ghost Data in Time Trials
Mii (Outfit B) - Unlock all 32 Expert Staff Ghost Data in Time Trials
Toadette - Play Time Trials on all 32 different courses or win 1000 Wi-Fi matches

And the different unlockable bikes/karts:

Magikruiser (small bike) - Play Time Trials on 8 different courses
Spear (large bike) - Unlock 12 Expert Staff Ghost Data in Time Trials
Sprinter (Medium Kart) - Unlock 24 Expert Staff Ghosts
Tiny Titan (small kart) - Beat 50 opponents during Wi-Fi play or unlock one expert staff ghost

hey thanx

You're welcome ^^.