Somme user difine their own DNS servuer. so the DHCP wont change it. look at IP settings on the users machine ipconfig /all and look if the DNS is the good one.
if it is good look in the host and lmhost file if the web sites are reference their. if it is chagit. I’v seen some virus that were changin the host file so the anti-virus can’t update. that is smart.
try to do a nslookup “your web site” to see wheir is it trining to translate the adresse. also see if Internet explorer had proxy setting. if their not good IE wont work.
Do you use a proxy server ? If so, the problem won’t probably be DNS related. In this case, make sure you have the correct proxy settings, and that the site is not included in the proxy’s exceptions.
If you don’t use a proxy, try a nslookup as suggested above, or a ping to the site, to see if the address is being resolved correctly. You can also do this on the DHCP server, write the ip address of the site, and try to access the site from your desktop by using the ip address (not the url). This will help to determine if the problem is a bad dns server setting.
above didn’t help