You’ll want to backup all your data (try CloneZilla) prior to any kind of major HDD edit. As a bootable set of utilities I recommend Hiren’s BootCD Hiren’s: http://www.hirensbootcd.org/download/
1. Backup your important files on C and F
2. Using Hiren’s, boot into “Parted Magic (Linux)” and use GParted to delete the WinXP partition.
3. Continuing to use GParted expand your other partition to encompass the newly liberated space.
4. Reboot, Using Hiren’s, boot into MiniXP and Use BootICE to reinstall your MBR and PBR to the active partition
5. Continuing to use MiniXP, defragment the disk
6. Reboot without booting to Hiren’s
7. Run the following commands in CMD prompt to clean-up the installation, being sure to replace “C” with the drive letter of your active partition, it’s best to still use F.