Mt Lassen - Summer, '10

Currently, the Devastated Area is plowed, and open. This gives access to the NE side of the mtn.  This yr., the Park road will open (completely)sometime by the beginning of July - due to a large snowpack.
The Summit trail will be undergoing construction, as there was an accident on the trail last summer. It sounds as though the work will be extensive. The California Conservation Corp (CCC) will be assisting with the work. The trail will be closed at times, once the road opens for the summer. You can check the times on the Park's website.
The trail offers excellent access to the various aspects of the Mtn.