The glibc package contains a FAQ with additional information that you should check if you are having problems. An online version is also available at http://www.imaxx.net/~thrytis/glibc/glibc-FAQ.html. Below are some tips for solving problems which are not covered in the FAQ or are covered here in more detail.
Glibc 2 uses a different method than libc 5 in looking up host names.
The glibc name server switch (NSS) code looks for a file
/etc/nsswitch.conf. If host names are not resolving for you
when using a glibc 2 application and your /etc/resolv.conf is
configured correctly, check if you have the /etc/nsswitch.conf
file. If you do not have this file, you can create one containing the
line:
hosts: files dns
/etc/resolv.conf to find the nameservers.
You should look at the section of the libc info pages describing the nsswitch.conf file for more details.