If you get the astros email blasts, then you should get a password that allows you to purchase tickets on Thursday.
Here's what the email stated:
The 2010 baseball season marks the 45th Anniversary of the Houston Astros. Join us as we salute Houston's rich baseball heritage in a season-long celebration.
For the last 45 years, our fans have been vital to the success of the Houston Astros, and as a thank you, we'd like to offer our astros.com subscribers an exclusive presale opportunity on Thursday, February 18, 2010. Beginning at 9 a.m. CT on Thursday, you will be able to purchase single game tickets to all 2010 Astros regular season home games before they go on sale to the general public on Friday, February 19th at 9 a.m. CT.
To access this exclusive presale offer, you will need to order online using a special astros.com presale password. Your password will be provided to you via e-mail early Thursday morning.
Buy Tickets Thursday at 9:00 a.m. CT »
To order tickets, click on the link above, then click on the link of the game you would like to purchase tickets for and enter your password in the box labeled "Presale" on the ticket ordering page. Please note, the online presale ends on Thursday, February 18, 2010 at 6 p.m. CT.
For Opening Day on Monday, April 5th against the San Francisco Giants, there will be an eight-ticket limit. If any account purchases more than the limit, the seats will be removed from the account and the proper refund given. For all games, excluding Opening Day (April 5th) there will be a 19-ticket limit. Tickets are limited and not all tickets are guaranteed.