I have a 95% OS X server shop..and just a handful of Windows servers I occasionally have to mess with... I need to resize some disks on a Windows 2003 box, and am looking for the equivalent of OS X's Disk Utility, if there is such a thing built into Windows 2003 server...Disk Management is not a part of Windows 2003 I am assuming?
"Disk Management" in the Computer Management console is the GUI version of diskpart's functionality - you can resize partitions and perform similar functions from there.
As a gotcha, Windows 2003 can't resize the System partition, you'll need something else for that (or to boot another install of Windows).
Right-click "computer" hit "manage" then enter the disk management node... when and where the expand features was added to the disk management UI however I'm not sure of, it always feels like diskpart is one step ahead of the UI on that in any Windows version.
You can try GParted:
There is a nice PowerShell-Gui (also for Win-PE) out there:
For more advanced partition resizing i recommend using free third party tools either for installation on windows or live-system booting into a cd/dvd/usb (list only for example not for complete reference!)