Hi everyone

I've got a Dell laptop here that I really want to set up to triple boot Windows 7, Ubuntu and OS X. I've found numerous tutorials explaining how to do this and giving various workarounds for one of the operating systems failing to start due to an overwritten bootloader, etc. But they all assume that the computer in question has enough room for the necessary three partitions (since you can only have a total of four.)

My computer already has three partitions, all of which are primaries, and I really don't know whether I can get rid of or merge any of them.
The first is an 'OEM Partition', it is only 39 MB in size and is hidden. According to a Lifehacker tutorial that discusses dual booting Windows and Ubuntu, this partition (up to 100MB) is found on most computers. They just ignored it. I am assuming that it's somehow necessary to the operation of the computer - is that true?

The second is 17.58 GB and is the 'Dell Recovery Partition'. My understanding of this partition is that it's supposed to contain files necessary to restore a Dell computer to its factory state by using a utility that's installed on the operating system partition. However, Partition Wizard lists it as Active, Boot. I have absolutely no idea why my recovery partition is set as the active partition. I had thought, before I saw this, that I might be able to image this partition onto an external HDD, wipe it and merge it with the OS partition, but I guess if it's set to Active it must be more important than I thought.

The third is OS (C, 578 GB, containing the Windows 7 Pro 64bit operating system and all my files and folders.

Can anybody shed some light on why my computer boots off the Recovery partition? Also, can anybody advise me on how to reduce the total number of partitions so I can create one for Linux and one for Mac? I'm thinking I may have to use an extended partition to get a shared files one in there.

Thanks for any advice you have for me!!