change from mx to us repositories?

[Brendan Miller]

For some reason when I installed ubuntu I was pointed at the mx
repositories. I tried editing all the entries in /etc/apt/sources.list
to point to us.archive.* but apt-get update seems to ignore the
changes:

Output of apt-get update:
Hit http://mx.archive.ubuntu.com jaunty Release.gpg
Hit http://security.ubuntu.com jaunty-security Release.gpg
Ign http://mx.archive.ubuntu.com jaunty/main Translation-en_US
Ign http://security.ubuntu.com jaunty-security/main Translation-en_US
Ign http://mx.archive.ubuntu.com jaunty/restricted Translation-en_US
Ign http://security.ubuntu.com jaunty-security/restricted Translation-en_US
Ign http://mx.archive.ubuntu.com jaunty/universe Translation-en_US
Ign http://security.ubuntu.com jaunty-security/universe Translation-en_US
Ign http://mx.archive.ubuntu.com jaunty/multiverse Translation-en_US
Hit http://mx.archive.ubuntu.com jaunty-updates Release.gpg
Ign http://security.ubuntu.com jaunty-security/multiverse Translation-en_US
Ign http://mx.archive.ubuntu.com jaunty-updates/main Translation-en_US

What's worse, adding new packages now completely fails:

sudo apt-get build-dep firefox
apt-get: build-dep firefox
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Could not open file
/var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_jaunty_main_source_Sources
- open (2 No such file or directory)

If I look in /var/lib/apt/lists I see:

ls
lock
mx.archive.ubuntu.com_ubuntu_dists_jaunty_main_binary-amd64_Packages
mx.archive.ubuntu.com_ubuntu_dists_jaunty_main_source_Sources
mx.archive.ubuntu.com_ubuntu_dists_jaunty_multiverse_binary-amd64_Packages
mx.archive.ubuntu.com_ubuntu_dists_jaunty_multiverse_source_Sources
mx.archive.ubuntu.com_ubuntu_dists_jaunty_Release
mx.archive.ubuntu.com_ubuntu_dists_jaunty_Release.gpg
mx.archive.ubuntu.com_ubuntu_dists_jaunty_restricted_binary-amd64_Packages
mx.archive.ubuntu.com_ubuntu_dists_jaunty_restricted_source_Sources
mx.archive.ubuntu.com_ubuntu_dists_jaunty_universe_binary-amd64_Packages
mx.archive.ubuntu.com_ubuntu_dists_jaunty_universe_source_Sources
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_main_binary-amd64_Packages
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_main_source_Sources
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_multiverse_binary-amd64_Packages
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_multiverse_source_Sources
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_Release
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_Release.gpg
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_restricted_binary-amd64_Packages
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_restricted_source_Sources
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_universe_binary-amd64_Packages
mx.archive.ubuntu.com_ubuntu_dists_jaunty-updates_universe_source_Sources
partial
security.ubuntu.com_ubuntu_dists_jaunty-security_main_binary-amd64_Packages
security.ubuntu.com_ubuntu_dists_jaunty-security_main_source_Sources
security.ubuntu.com_ubuntu_dists_jaunty-security_multiverse_binary-amd64_Packages
security.ubuntu.com_ubuntu_dists_jaunty-security_multiverse_source_Sources
security.ubuntu.com_ubuntu_dists_jaunty-security_Release
security.ubuntu.com_ubuntu_dists_jaunty-security_Release.gpg
security.ubuntu.com_ubuntu_dists_jaunty-security_restricted_binary-amd64_Packages
security.ubuntu.com_ubuntu_dists_jaunty-security_restricted_source_Sources
security.ubuntu.com_ubuntu_dists_jaunty-security_universe_binary-amd64_Packages
security.ubuntu.com_ubuntu_dists_jaunty-security_universe_source_Sources

so a bunch of explicit references to the mx repo.... how do I tell apt
to fix this and point at the right repo?!