It would appear that Snow Leopard 10.6.0 has an issue with client-sideDNS resolution. Symptoms include erratic resolution of domain names from local network DNS servers for any command or application using gethostbyname(). However, using the host or nslookup commands resolve things correctly.
The current best resource for this issue is a thread on the Apple support forums. There are all kinds of suggestions as to what the problem is and all kinds of voodoo fixes, though none have been found to work for most (or all). I’d hold off on attempting these untill 10.6.1 rolls out, which will be in the near future.
In the meantime, i’d suggest using your /etc/hosts file for must-have names. Keeping an eye on that thread may shed further light on the situation as the problem is investigated in greater detail.