...and would like to vote in the upcoming primary, make sure to go here, and follow the directions under "Download and Mail a Voter Registration Form" to re-register this week before the deadline passes next Monday. You may want to use priority mail to send the form in, or even hand-deliver it to your county's Registrar of Voters.
ETA: I think it's too late to register as an absentee voter; if I'm not mistaken, they've already started mailing out the absentee ballots. If you want to register absentee, you should probably wait til after the primary; you don't want to be listed as an absentee voter in the rolls at your precinct, but not have an absentee ballot either... If re-registering is the only way to get in on voting in the Dem primary, you could go ahead and do it anyways; you'll probably just end up voting a Provisional Ballot (which they should count once they verify that they received no mailed-in ballot from you). Apparently the fact that they've already started mailing out absentee ballots doesn't mean absentee registration is closed... Still, I personally wouldn't want my franchise dependent on the postal service having a turnaround of under a week. I'm really surprised they let you switch to absentee status that close to the election.
Also, the voting methods apparently still vary more, from county to county, than I'd thought. Google "Blah Blah County Registrar of Voters" if you want details for your own location, I just know what we've done in Santa Clara County.