You might want to post this in the Gaming board section of this forum located here:  Gaming/My Games.  The regular posters there are very familiar with gaming issues; since you said that World of Warcraft runs "perfectly," this may be an issue with Starcraft itself.  Hopefully someone over there can help. 

 

Be sure to list your exact computer model, memory, and connection method.  All of that information will be helpful to them in diagnosing and potentially correcting your problem.  Good luck.