Pokemon Heart Gold and Soul Silver - Walkthrough - Viridian City Pokemon Heart Gold and Soul Silver: Walkthrough - Viridian City
We can't fight the Gym Leader yet, but check out the TRAINER HOUSE in this area. We're passing by, so heal up.

There is a body of water on the left side of the city with a man on the other side, SURF across and talk to him. You will get TM85 DREAM EATER.

Now, exit the city south.
This walkthrough was written by MKaykitkats, used with permission.