How to reformat WD Passport External HD?

I bought a WD Passport External HD for my PC and will be making the switch to iMac soon (next month), what, if anything, do i need to do to reformat this thing so that it will read and write with my mac?

according to WD website it is compatible:
Available USB port

Windows® 2000/XP

Available USB port

Mac® OS X 10.1.5+

Windows 2000/XP

Compatibility may vary depending on user’s hardware configuration and operating system.

So could someone walk me through of how I could reformat it so that it would be usable (read and write) on both my PC and my MAC.

How is it now formatted? My Passport came in FAT32. If yours is that way it will work fine in OSX. If it's in NTFS, NOTHING but 32 Bit Windows will Write to an NTFS drive, but OSX will read the drive. If it's in NTFS, I would back it up and format in FAT32. That way everything can read it. The problem is if you are in XP is XP will not format drives FAT32 over 30+ GB. You can do it on the Mac when you get. Check and see if it's not already FAT32.

All my external hard drives are formatted HFS+, and I use MacDrive on my PC to read & write to them.

http://www.mediafour.com/products/macdrive/