There is an issue with Mac OS X 10.6.0-10.6.2, where the order of DNS server entries may be read in the reverse order.  This can occur if the DNS server entries are added in the Network system preference pane, or if the DNS servers are provided by a DHCP server.

An unresolved bug report has been filed with Apple (#6928835), and it is marked with the description of “Mac OS X internal name resolution often uses DNS servers in reverse order”.

This behavior can cause unexpected results, especially if you have a DHCP server that is providing one or more internal DNS servers, in addition to an external DNS server for a fallback (which is typically listed last).