I own a Mac and I want to install a triple boot. The problem is that I need to keep my windows bootloader to make sure that it works well with Mac OS. But I want Ubuntu too and if I install ubuntu, it will install Grub on the MBR. In previous versions of Ubuntu, it was possible to choose where installing Grub but I can't find it in Ubuntu 11.10. Is there someone who knows how to do it ?
Ok it seems that it is not a problem of MBR in my case. On a Mac there are GPT and MBR. You must use the Disk utility of Mac OSX to make all partitions because this is the only tool which is able to synchronise GPT and MBR (they are note made to work together, it is usually one of them). I think it was my problem because I succeed, even in putting grub on the MBR. Thanks for your help mikewhatever !
Select manual partitioning and you'll see the option to select where to install Grub.