I would argue that it is simpler and better to stay with a single partition; much easier to manage the overall space then. Here is my oft posted run down on the options you have available for that single partition:
Both Mac and PC now support four common file systems:
1/ FAT32 - The older, lesser Windows standard file system
2/ NTFS - Win NT, 2000, XP and Vista all default to this
3/ ext2/3 - Mac, Win and Linux all share this format
4/ HFS+ - this is the native Mac OS X format.
Here is how to do each one:
1/ FAT32 - this is supported natively by both Windows and Mac. Just format your drive for it and both Win and Mac can read and write. Drawbacks? It has no file permission model, making it somewhat insecure, plus causing the loss of Mac OS X's carefully crafted per file permissions as you transfer things back and forth. FAT32 is "cheap and cheerful", but not recommended.
2/ NTFS - This has been supported by Windows for a long time, and has just very, very recently become available in full read/write mode for Macs. See the following thread, by Paragon Software, advertising beta availability of their NTFS for Mac:
http://www.mac-forums.com/forums/showthread.php?t=76246&highlight=Paragon
This *is* beta, and it will be shareware, but first reports are that it works very well. Previous file system offerings from Paragon seem very well regarded. They have been in the file system driver business for a lot of years.
NTFS does have a more mature permissions model than FAT32 and is generally more secure. This option is better than the first one.
3/ ext2/3 - this is the standard Linux file system. Both Windows and Mac have installable file system drivers for it. For the Mac, see this:
http://sourceforge.net/projects/ext2fsx
and for the PC, see this:
http://www.fs-driver.org
ext2/3 is an extremely mature, fast and very well regarded file system. It supports pretty much the same full file permissions model that HFS+ does (both, after all, are *nix based file systems), making it a recommended solution. Both the Mac and PC drivers are free, so that is attractive too.
4/ HFS+. This is the Mac standard system. To enable this for the PC, you need to get MacDrive. This mature and well regarded piece of software adds seamless support for HFS+ to your PC. If you are willing to spend the money, it may be the best solution of all.
So, there you have it. LOTS of ways to share your hard drive between your PC and your Mac.