Software :: Login Loop After Shutting Down Computer During Update Install

I recently installed Leopard. On my way to bed I saw that there was an update to be installed. I clicked install, but the install took to long (and was being executed in a special screen after the shut down of the computer, so there were no annulation options) and I was so annoyed with the length of the installation that I shut my computer down. A big no, so it seems, because the next morning when I booted my computer, the login screen appeared. I set up-auto login, so seeing a login window was strange. When I entered my correct password, I first saw a blue screen and then returned to the log-in screen. There appears to be no way for me to log-in.

Things I've tried: safe boot, booting with the install DVD (I checked the harddrive for any problems, there were none) and booting while pressing an interesting variety of keys. With the same result: none. I tried doing the root-user thing, but to no avail. I think I don't have root user selected in finder. The updated I tried to install was the last one seeded by apple, I think it was the 10.5.3 update; there were three files to be installed. My computer is and intel iMac from the first quarter of 2007.