How to disable a particular PPA?
Hit Alt+F2 and run software-properties-gtk.
Click on Other Software tab, you'll see that each PPA have two lines here, one for the compiled packages and one for the source, Uncheck both lines to disable a PPA.
I would just comment it out in /etc/apt/sources.list like this...
# deb http://archive.canonical.com/ubuntu natty partner
# deb-src http://archive.canonical.com/ubuntu natty partner