Noob question regarding git push

Hi All,

So I have a central build repo from which we perform nightly builds.
Then my development repo is a clone of the build repo. The idea is
that after I am convinced that my changes in my development repo are
stable enough I push them to the build repo using git push.

This seems to work and I can see my changes when doing a git log from
the build repo. However, the actual working files have not been
updated nor can I figure out any way to get them updated. For instance
I have tried deleting one of the files that should be changed and then
doing a git checkout <file>. The changes are still not present. I have
tried doing a git reset --hard HEAD. The file still doesn't contain
the changes. I have even tried checking out a different branch in the
build repo and then re-checking out the master that should have those
changes. Still nothing.

What's the proper technique for making sure you see the actual changes
that were pushed to a repo?

This is debian lenny with git version 1.5.6.5.

TIA,
-Harry