I found that when instaling Ubuntu (Dapper Drake) on an imac after the install starts you hear music but the screen is black / blank. Here is how to fix that problem
- ctrl+option+F1 (This brings up a command prompt)
- type: sudo nano /etc/X11/xorg.conf
- Find the line that says "Load dri" and place a # infront of the text
- Find the line that says "HorizSync" and change the value to 60-60
- Below edit the line "VertRefresh" to 75-117
- hit Ctrl+O, it will ask where you want to save, just hit enter
- hit Ctrl+X, this will bring you back to the command prompt
- Type sudo killall gdm
- Type sudo /etc/init.d/gdm start
At this point the GUI will load and you should be clear to load the install or use the LiveCD.