This is something I've thought about a lot since my switch to linux. as much as I try to shy away from anything Windows or Microsoft related, the best type of partition to store shared data on in my experience is NTFS because can be mounted as read/write in all major operating systems (Windows, Linux, BSD, and Mac OSX). I create small primary partitions for my operating systems in whatever file system they require, and then one large extended NTFS partition to use as a communal storage for files. Then I configure my "home" or "My Documents" folders to point to that drive. On Mac and Linux just delete the folders from your home and then create symlinks to the folders on the NTFS drive, and add the NTFS drive to your /etc/fstab. On Windows XP use Winbolic to junction to them or on Vista/7 just change their target in file properties.
That way the same data is accessible from whatever OS you're booted into at the time.
Here is the output of fdisk -l on my netbook
if you plan on multibooting, partitioning your drive is the first step. You should plan out how you are going to set up your computer before you install any operating system. It should never be an after thought. And if you plan on multibooting Windows with Linux and any other OS (Mac OSX in my case) you should make sure you have proper install disks for each OS, ie; NOT RECOVERY DISKS. Although it's possible to start from a factory install of Windows, because of the modifications that manufacturers do to the OS and partitions can cause all sorts of headaches when trying to install addition operating systems.
Disk /dev/sda: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00048e47
Device Boot Start End Blocks Id System
/dev/sda1 63 58855958 29427948 af HFS / HFS+
/dev/sda2 58857472 121772031 31457280 7 HPFS/NTFS/exFAT
/dev/sda3 * 121774078 488396799 183311361 5 Extended
/dev/sda5 121774080 153231359 15728640 83 Linux
/dev/sda6 153233408 484202495 165484544 7 HPFS/NTFS/exFAT
/dev/sda7 484204544 488396799 2096128 82 Linux swap / Solaris