I'm installing Ubuntu 13.04 onto my 32-bit Intel Core 2 Duo CPU, from a live-usb. One of the screens says "Installation type", with the three options "Install Ubuntu alongside Windows Vista" or "Replace Windows Vista with Ubuntu" or "Something else". No matter which of those three options I highlight, the "Continue" button is always grayed out and un-selectable. (I can only select "Quit" or "Back".) (When I highlight the second option, the word "Continue" switches to "Install Now" on the button ... but it is still grayed out and unselectable.)

Other than the fact that I cannot "continue", the installer offers no information about what's going wrong. Any ideas? Thanks in advance!! [I am also happy to hear advice about how exactly I can file a bug report about this.]