Sonic & SEGA All-Stars Racing

Easiest way to do this is to start a match on 2 player with the second pad in use..... Race the second pad untill you completed one lap....... then race player one untillyou get an all star power up.......... then continiue untill just before the finish line then just as yu see it comming up use the all star......... then after the cutscene animation cross the finish like.......

Da Ding its yours.

Altered Beast

Go to single race and pick a character with a speedy All-Star Move like Sonic or Shadow. Pick any course and just say in the back for a while until you get an All-Star power up. Then race like normally. When you're near the end of the final lap, use the move and cross the finish line. Ding! Achievement Unlocked!