I'm not sure what date you want, but one of these links should work if you find the date of the original webcast. Webcasts are posted the same or next day on Live Meeting, Autodesk usually lags on posting the link to their website.
Performance Improvements from Civil 3D 2007 to 2008
Recorded: April 6, 2007
https://www115.livemeeting.com/cc/autodesklearning/view?id=Civil_RO-51&pw=Audience&cn=
Recorded: April 13, 2007
https://www115.livemeeting.com/cc/autodesklearning/view?id=Civil_RO-52&pw=Audience&cn=
Recorded: April 20, 2007
https://www115.livemeeting.com/cc/autodesklearning/view?id=Civil_RO-53&pw=Audience&cn=
Recorded: April 27, 2007
https://www115.livemeeting.com/cc/autodesklearning/view?id=Civil_RO-54&pw=Audience&cn=
Civil Reminders
http://blog.civil3dreminders.com/
http://www.CivilReminders.com/
Alumni