I received the dual boot ubuntu 8.04 disk and have somehow got myself locked out when it asks for a user name and password. It tells me the username or password is invalid and will not let me open the disk. Please help.

I would wipe it out using this http://www.killdisk.com/downloadfree.htm And do a reinstall.

I would not wipe the disk. I would first try to reset the password. See http://www.psychocats.net/ubuntu/resetpassword