You really should be keeping Kubuntu and removing Windows---oh well...
If you simply delete the Linux partition then you lose GRUB's configuration file--that is probably what caused the error you saw.
You can use just about any partition editor to remove the Linux partition(s). If your Linux installer is a "live CD", you can boot from that and remove the partitions from there.** And I think you said that you can remove the partitions from Windows.
You will then need to boot from your Windows intall disk---rescue mode, and run "fix mbr" to put back the Winodws bootloader.
**If there is no GUI tool, open a terminal and type fdisk -l. This will show you all your partitions. Let's assume you have one IDE drive--you will see several entries with hdaX, where X is the partition #. Now do fdisk /dev/hda. Enter "p" to list the partitions, and then "d" for delete. enter the partition number to be deleted. When done, enter "w" to save the changes and exit.