Wizard101 will be launching on Steam in the near future. The game will not be compatible with the standalone version, but most of the same services available at the current time will be available on the Steam version including family accounts, individual accounts, etc. One cool aspect is that all players share the same servers so Steam and standalone players can head out on adventures together!
To help fans and potential Steam players, KingsIsle has posted a handy FAQ:
Will I be able to quest with other players who are using their KingsIsle account?
All players use the same servers, using the same data, so all wizards will play together no matter what type of account they are using. If an existing player makes a new Wizard101 account on Steam, they can befriend and play with the same people from their prior adventures in the Spiral. Existing players using non-Steam KingsIsle accounts can play with new Steam users and show them around.
Check out the Wizard101 site to learn more.