How to move a drupal 6 installation to a new server?
Do you have mod_rewrite for Apache enabled/installed?  If not, verify this is the case.

Also, ensure that your .htaccess file in your Drupal root is unchanged from the old server.

If you're on a Debian-based distribution, go to /etc/apache2/mods-available to verify that rewrite.load is present.  Then go to /etc/apache2/mods-enabled to verify that rewrite.load is symlinked in that directory.

If you're on a RedHat distro like CentOS, then go to /etc/httpd/modules and look for mod_rewrite.so.  Then, open up /etc/httpd/conf/httpd.conf and verify that this line is in there LoadModule rewrite_module modules/mod_rewrite.so.