From your description, it appears that either there are no other partitions on the same physical drive besides C, or that you already have a backup of that data.
If this is the case, save yourself some time and trouble and use BootItNG shareware partition manager:
http://www.terabyteunlimited.com/bootitng.html
It works as a standalone boot disk, fairly easy to use and it allows you to resize partition in-place. I had resized about 20 different partitions with it with no ill effects.
Only ONE CATCH: after you boot using BootItNG CD or floppy, it will ask you if you want to install BootItNG to your hard drives. DON'T. Press "No" and go straight to Partition Management. If you say "Yes", nothing terrible will happen, but after evaluation period will expire, you won't be able to boot your computer without purchasing BootItNG.
First, back-up your partition with Ghost or BootItNG itself. They both back up partitions to DVD drives.
*If your DVD drive is external, in BootItNG you have to go to Options->checkmark "Enable USB2.0 support", "Enable Firewire/IEEE-1394 support"
Second, in BootItNG go to Partition Management->Manage Partitions-> select your HD, then your partition, click "Resize". As with any utility, you should have unallocated space adjacent to your existing C partition. Specify the new size. BootItNG will check drive for errors before and after the resize, just in case.