Circle dock is a self contained file/program, and no runtime installation is required.
Find where you placed the Circledock folder, and simply delete it!
If you have placed a shortcut to your startup folder you will have to delete this as well.
If you are running Windows Vista, you will need to go into your (Hidden) AppData file and delete the Circledock entry there as well.
In XP you will have to search for related Circledock file and delete, or use a program such as CCleaner or Advanced systems care.
I would run either Advanced Systems Care
to ensure that there is no tell tail signs in my registry. Use either of these products with extreme care.
You are responsible for the results, but I use them regulary.
This process will completely uninstall Circledock