Here are the details, I read about this in the Toys R Us catalogue about 20 minutes ago.
Toys R Us stores in Australia will soon be distributing special Jirachi’s to Pokemon Diamond, Pearl, Platinum, HeartGold and SoulSilver games via Mystery Gift. This Jirachi (which was distributed three months ago in the US at Gamestop stores) will also unlock a new “Night Sky’s Edge” PokeWalker Course in Pokemon HeartGold and SoulSilver.
Jirachi is at Level 5, holding a Liechi Berry and is obviously inside a Cherish Ball. The Jirachi knows the attacks Wish, Confusion, Rest and the special move Draco Meteor.
The event begins June 3rd 2010 and will end on June 13th so make sure you head down to your local Toys R Us store during that period.
I read in the Big W catalogue last night that they are also distributing Jirachi in the same way, so if Big W is closer to you than Toys R Us, you're in luck! (Both are just as close for me, but I know in my state of Australia there are only 3 Toys R Us stores and over 10 Big W stores, so it's a plus for some people). Head over to bigw.com.au/entertainment for the link for the details if you're not sure how to obtain Jirachi, I'm sure they'll have instructions instore, but to be on the safe side it wouldn't hurt to check up first.
I'm looking forward to getting myself 3 Jirachi's, and my fiancee will probably get 2, seeing as between us we have all 5 compatible games