All,
I downloaded/installed 1.9.2 windows installer, and then RubyMine3.0RC, and installed it.
Opening a new Rails project, with mysql selected as the DB, gi
Make sure you have libmysql.dll from the 5.1.x 32-bit MySQL distribution in PATH or in RUBY_HOME\bin directory.
If it doesn't help, you may have better luck reporting the issue at the mysql2 gem project homepage.