GPT partition table warning message during install of ubuntu

I am answering because the answers here are inadequate. I don't want future viewers of this question to destroy their windows partitions just to install Ubuntu.

To fix your problem, follow these steps:

1. Boot the emergency disk (Ubuntu or other linux Live CD) and open a text-mode shell.
2. Type sudo gdisk /dev/sda (change /dev/sda to whatever is appropriate to access your hard disk, if necessary). The program is likely to complain that it's found both MBR and GPT data, and will ask which to use. It doesn't matter which you tell it to use.
3. At the Command prompt, type x to enter the experts' menu.
4. At the Expert command prompt, type z to zap (destroy) the GPT data.
5. Type y in response to the confirmation about destroying the GPT.
6. Type n in response to the query about blanking the MBR. Caution: If you answer y here, you'll destroy your Windows partition(s)!

NO NEED FOR A EMERGENCY DISK!!

Simply boot with ubuntu live CD or USB (I did with USB).

Then open the Terminal. Type: sudo gdisk (hit enter) Type: /dev/sda (change /dev/sda to whatever is appropriate to access your hard disk, if necessary). Then you will probably see that there are MBR and GPT. Tell the computer you want to use the MBR Then: At the Command prompt, type x to enter the experts' menu. At the Expert command prompt, type z to "zap" (destroy) the GPT data. Type y in response to the confirmation about destroying the GPT. Type n in response to the query about blanking the MBR. Caution: If you answer y here, you'll destroy your Windows partition(s)!