Create the CNAME record "portal.domain.com" referring to "obscureServer32324name.domain.com" in the "domain.com" DNS zone. From a command-prompt, do a:
What do you get back?
Bear in mind that if "domain.com" is an Active Directory-integrated zone you could have a slight delay before the DNS server begins to resolve it.
Also on the Active Directory integrated DNS front, bear in mind that your DNS client might not be trying to resolve against a DNS server that's "looking at" the same copy of AD where you added the record (via DNSMGMT) a moment before. Force AD replication or wait 5 minutes for AD replication to complete.
You don't need to stop / restart the Microsoft DNS server for changes like this to "take".
Edit re: your comments:
Bizarre. I'm at a bit of a loss. That's a pretty common configuration, so it ought to work fine. I have several Customers with servers that are configured just that way (w/ CNAME records like "WSUS" or "antivirus", etc).
The computer you're testing from is configured to use the server computer where you added the CNAME as its DNS server-- correct?
Do the following, just be sure that you're querying out of the right zone:
nslookup -querytype=SOA domain.com
You should get back something like this:
primary name server = server.domain.com
responsible mail addr = hostmaster
serial = 425
refresh = 900 (15 mins)
retry = 600 (10 mins)
expire = 86400 (1 day)
default TTL = 3600 (1 hour)
server.domain.com internet address = 192.168.1.1
Be sure the SOA record that you get back really is referring to the server computer you expect to be seeing the zone hosted from.
We'll figure it out, it just may take a moment.