I need to reclaim some disk space for a little while, but need all my data and I've run out of blank dvd's.

I'm going to remove fedora core 4, but I can't remember whether or not it is safe just to delete the partitions from disk management in XP. If I do this, I would have thought it would hurt the grub bootloader, probably fatally. Is this going to stop my computer booting to windows? will I have to reconstruct the MBR using the XP recovery console?

Yes, deleting the Linux partition will break GRUB. And yes, you can reinstall the Windows bootloader using Recovery Console.