LiveCD - Gparted = wipe it out. Keep it simple :D

I dont know about extending the partition all the way out again.. never
done that before but, what you could do is wipe out ubuntu, create a
second windows partition and put your My Documents over there.

I didn't think of just making it a new "My Documents" partition. It's a
good idea and I'll consider it before I do anything.

Other than what you suggested, did the rest sound ok for reverting the
machine back to Windows??

If you are using FAT32 then gparted will allow you to expand the existing
Windows partition without loss of data. If it's NTFS you will need to
acquire something like Partition Magic to do this.

Gparted can resize or delete NTFS partitions also. But it is so slow if the
partitions are big and loaded...