You come across Hippaul in what used to be Disk 3 (out of 4) of the game, when exploring Alexandria as Vivi for the second time. That will be your only chance to do this mini-game, so finish it before you progress with the story. You can find Hippaul and his mother in a street south from the plaza with the ticket stand (the same street where we first got to control Vivi at the beginning of the game).

You talk to the mother to race Hippaul. As you win races, Hippaul's level increases. You can talk to Hippaul to find out what his current level is.

If you win a race by a lot, Hippaul gains 5 levels. If you only just beat him, he'll gain one level. Every 10 levels up to level 80, you'll gain a reward. The first seven are cards, the last is the key item Athlete Queen. Upon obtaining it you'll gain the Track Star achievement.

Level 10 Wyerd Card
Level 20 Carrion Worm Card
Level 30 Tantarian Card
Level 40 Armstrong Card
Level 50 Ribbon Card
Level 60 Nova Dragon Card
Level 70 Genji Card
Level 80 Athlete Queen

You can continue racing beyond level 80 up to level 100 but there aren't any rewards.
If you max out your cards inventory in the middle of playing this, just delete some of them to free space, and the next time you beat Hippaul in a race you'll receive the card you weren't able to earlier.

Hippaul will get harder to beat as he levels up, but believe me, any n00b CAN get to level 80, and now for some tips how!

Racing consists of pressing two buttons alternately. Follow these steps:

1. Use the keyboard for this, rather than your controller.
2. Rebind the keys (Menu, Config, Manual, Keyboard) so that the Talk and Dash keys are right next to each other, so you can hit them with your index and middle fingers.
3. You'll probably need to swap hands throughout, feel free to rebind keyboard keys each time you do so for comfort. I used 'Z' and 'X' for my left hand, and ',' and '.' for my right.
4. Autosave every now and then by exiting and re-entering the screen (eg. by entering and leaving the nearby doorway)
5. The main thing to fight is tiring your hands/arms out. Keep your arm at a comfortable 90º angle, the forearm resting on a flat surface. When you begin losing a lot with one hand, swap to the other, it'll make a huge difference. You can always save and come back later refreshed as well.
6. Make sure you lift your fingers enough to clearly differentiate between the two button presses, because if you keep one pressed while pressing the other Vivi will stop abruptly.
7. I recommend to jump the gun and start pressing buttons a bit after "Get set!" to get into the rhythm of it just before the race starts.

Remember, beating Hippaul by a lot means jumping 5 levels instead of 1, so that should make the first 50 or so pass quickly.

There will be a Mognet letter in Treno about the racing. If you beat level 60, it will say 'Vivi'. If not, it'll say 'Hippaul'.
The cards you win here will be very useful for the card competition in Treno.
Having Athlete Queen counts towards your treasure hunter's rank.