Backup your data and boot from a Linux rescue CD. Use the free partitioning software to expand C and delete or minimize D. If you installed programs on D, you have to reinstall. If it's data, just move it. It may contain your recovery partition, so if you have to reinstall windooos, you'll have to have a disk with SP 2 for SATA support (if needed) and do it from scratch. Or just reinstall Windows and change your partitioning.
Linux recovery CD's are free to download as an iso is set to boot from CD. and burn. Make sure your BIOS is set to boot from CD.