Hi White_Eskimo!
I really don't know what exactly have happened, since I never used YDL, but here is what you can do:
- Either use text based fdisk or
- Partition your hard drive with disk utility from MacOS 9 cd.

Since you will be repartitioning your hard drive, you would have to (re)install both MacOS and YDL, cause resizing isn't possible for Apple files systems. Make sure you install MacOS 9 first.