Official Sega Dreamcast Magazine: Demo Disc 3 Cheats
for Dreamcast

Extra fight for Street Fighter Alpha 3

First, select the Network option. Then select the Dojo.
Next select JOIN. Select the character that you want to fight with
and exit. Go into the GR match and select the
first (and only) option it gives you.
You will fight Dan, but be careful-he has a tremendous
10-12 hit combo.

Grenade in Zombie Revenge

When Fighting the big boss, walk to the upper left and stand by the box
wait for him to hit you to the ground, breaking the box open and whalla a
grenade. (throw it by pressing punch)