I would not go by the tutorial because you are liable to lose all your data and OS. Do this:
1. Delete the partition that you last created - e.g. with Disk Management. Now you should have only 4 partitions.
2. Download
PW422 from here. Burn that to CD (e.g. with ImgBurn) and boot with that CD.
3. Now reconvert the dynamics with PW.
4. Convert the C partition from primary to logical. That can also be done with the PW CD - controls are in the Partition tab > Modify. You have to highlight the partitions you want to change.
5. Now you can create an additional logical partition without running into the dynamics.