Macbook Air + Lion + Windows 7 Boot Camp + shared partition
Ok, this is written for a 500GB HDD.
4 partitions max, just like every other (bootable) hard-drive.

I tried this on 2 MacBook Pros and it works perfectly on both.

This tutorial also assumes you have OS X Lion installed.

What I want to achieve is to have OS X Lion &amp; Windows 7 installed, with a shared space too.


120 (OSX)
260 (SHARED)
120 (Windows)


------------Part 1/2------------

Start off by resizing Mac OS X Partition so it's at least 1GB smaller than the full disk.

To do this; go into Utilities and then into Disk Utility. Select your HDD and go to the Partition tab.

1GB is not actually needed, but it's just to be on the safe side, it'll get resized later.
There needs to be 'Blank' unallocated space available.

What you originally have (factory settings):

 diskutil list


500GB:


disk0s1 EFI (Boot) ~200MB
disk0s2 Mac OS X 10.7
disk0s4 Mac OS X Recovery


disk0s4 needs to be deleted. Go into Utilities, and load up Terminal.
Type the following:

diskutil eraseVolume HFS+ Blank /dev/disk0s4


Then go into Disk Utility and delete the 'Blank' Partition.
You should only have your OS X Partition and blank space.

Then check your partitions with the command 'diskutil list', you should now have:

500GB:


disk0s1      EFI (Boot) ~200MB
disk0s2      Mac OS X 10.7


GOOD!

This part was referenced from: http://osxdaily.com/2011/06/30/deleting-the-mac-os-x-10-7-lion-recovery-hd-partition/

------------Part 2/2------------

Stretch OSX to the full available space using Disk Utility.

Load up Bootcamp Wizard, make Windows Partition 120GB whilst OSX has the remaining 380GB.

Bootcamp should be happy to start the install, but load up Disk Utility first

NOTE: On Lion 10.7.2, Bootcamp has changed a little. You need to insert the Windows 7 disk and then proceed with the installation before the Bootcamp partition will be created. When your computer restarts you need to hold down the option (alt) key and boot back into Lion, then follow the steps below:

Select the OSX Partition, and '+' another partition.

Reduce OSX to 120GB and make the new (middle) partition MS-DOS FAT, call it SHARED. That's what I'm using for now.
Whilst FAT doesn't allow for any single files over 4096MB; it's also writable natively with both OS's.

It should be 260GB. Now you have:


120 (OSX)
260 (SHARED)
120 (Windows)


According to Disk Utility, but...
In reality what we have is:

500GB:


disk0s1      EFI (Boot) ~200MB
disk0s2      Mac OS X 10.7
disk0s3      SHARED
disk0s4      Windows 7


Insert Windows 7 disk (if you haven't already) and then start the install sequence.

You'll notice that there's a 128MB unallocated space. Tragically you'll have to leave that unallocated.

Format the BOOTCAMP partition (only) and proceed to install Windows.

Don't mess about with deleting and merging partitions, otherwise the partition tables will be damaged.

------------DONE------------