Instructions
Catch a Ditto if you don't have one already. In "Pokemon SoulSilver," Ditto can be found on Routes 35 and 47, the Cerulean Cave and at the Safari Zone.
Take Ditto and Glalie to the Pokemon Day Care on Route 34 and leave both of them with the day care attendant.
Walk around for a while, perhaps training your other Pokemon to pass the time, then head back to the Pokemon Day Care.
Speak to the old man standing outside the Pokemon Day Care to receive the egg. The amount of time it takes to get an egg can vary, with some Pokemon breeding more quickly than others, though the chance is calculated every 256 steps. Be patient if they don't produce an egg immediately and walk around some more until the man gives you one.
Walk around until the egg hatches, which should take about 5,355 steps. If the newly hatched Snorunt is male, repeat Steps three through five until you get a female Snorunt. If your new Snorunt is female, proceed to Step six.
Use the Dawn Stone on your female Snorunt to make it evolve into Froslass.