Title says it all. This file doesn't appear in 'apt-cache search'.
deb http://ftp.us.debian.org/debian squeeze main non-free contrib
How do I get this installed? Do I have to build from source?
No binary valgrind packages are available for arm apparently. You'll have to build it yourself with the following command:
apt-get -b source valgrind
If that fails, look at the output and make sure you have met all dependencies. If not,
sudo apt-get install those dependencies and try again.