If you know anyone who has not updated and needs 1.5.5 to access SL and cannot receive the update (or access this forum) because of the ongoing DOS attacks and the moving around of IP addresses, the installers are being hosted on SLUniverse.com. For more information, refer to the announcements forum at http://www.sluniverse.com . The Windows and MacOS clients are both available.
Specifically, the announcement is here:
http://www.sluniverse.com/forums/shwmessage.aspx?ForumID=20&MessageID=3612
