Go to System Preferences --> Users & Groups and turn off the Guest account.
I use CandyBar to change Mac icons however the applications Sparrow, iPhoto, and iMovie have a lock and I can't seem to change it. Anyone know how?
Do you happen to have bought those apps from the App Store?
Yes, Sparrow is from the App Store. iPhoto and iMovie as you already know came pre-installed.
Candybar does't support changing App store icons. Although you can do it manually.
I use LiteIcon and no problem.