For GParted you will first have to get familiar with the Linux tool there for a good free drive utility. In order to use that you need two things right away namely a cd writer and the free version of BurnOn will work quite well for burning the iso disk image onto a cd-r not cd-rw for this. Once you burn the 35mb iso image onto a now bootable cd-r you either press the F8 boot device options menu if your board has that seen next to the key used for entering the bios setup or go into the bios to change the boot order to cd rom.
On a one drive system and XP you can't use the Disk Management even for resizing the D partition let alone the C primary. This is why a floppy or cd type tool and a boot from removable media will be needed. The 0.3.3.0 live for cd version of GParted is the one for use on a Windows machine being "platform independent" and the best of the few available that will work for MS partition types.
The typical screenshot of GParted can be seen at
http://gparted.sourceforge.net/larry/livecd/screenshots/gparted-livecd-0.3.4-5.jpg while the main download page for all live for cd versions is seen at
http://sourceforge.net/project/showfiles.php?group_id=115843&package_id=173828 You have to go down to the #13 item seen to get the 0.3.3.0 version. Simply click on the plus sign next to the item to open up the information and see the link on the far right side. Make sure it says "platform independent" since the others won't work on MS.
For burning an iso type image to disk and a good free version that works well for burning GParted onto a cd-r you can grab a copy of BurnOn at
http://www.burnworld.com/burnoncddvd/
Once you have a copy burned on disk and are ready to boot from it simply press the enter key at each of the four prompts to avoid getting lost there. The 24bit setting is normal for GParted since this is a Linux tool. The 1024x768 resolution seen default is the actual best to keep everything onscreen in view. When the 1280x1024 was tried the tab for selecting drives was offscreen.
Once you get to the main gui as seen in the screen shot at the first link for GParted you will see HDa1 as the drive listed and with a quick look below the menu bar you will see the two NTFS type partitions listed one above the other. To first shrink the D you first click on the "resize" button seen on the menu bar and select that partition. There's a large slider bar on the screen you can click and hold on rather then using the small arrow keys to increase or decrease a partition's size.
Once done you simply click on the apply button and answer yes to the confirmation prompt. For you the first thing and best thing if you use GParted is to practive a dry run simply to get familiar with how it works. After actually using it a few times it becomes second nature fast while confusing at first.