If you double click "my computer", then double click on C drive, then on programs, you should then see the CCleaner folder. Right click and delete the folder, then delete it from the recycle bin.
If for any reason it won't let you, try in safe mode. In case you are unsure about using safe mode here are some instructions
http://www.pchell.com/support/safemode.shtml
Here is a direct link to the setup, remember to choose whether or not you want the yahoo toolbar, you have a choice.
Download the setup to your desktop and try and install.
Let us know how you get on