Name Lookup of Enterprise Manager

Hello!
I have noticed a strange behaviour of Enterprise Manager (or every
program to connect to SQL Server; as in Visual Studio, Query Analyser
and ODBC-Connection Manager), which I cannot get sorted out.
I try to connect to an MSDE-Instance on a clients' Server. The Server
has, for our Maintenance, a dial-up connection with dynamic IP and
runs a service to keep the IP up-to-date, so we can access it by
servername.dyndns.org.
I can ping the server and I can connect to it in pcAnywhere (using the
dyndns.org lookup).
If I try to connect to the MSDE as servername.dyndns.org\Instance, I
get an error: Server not found: Connection.Open(Connect()).
Trying to make an ODBC-Connection gives some numbers on the error:
SQLState: 01000
Server Error: 11004
followed by
SQLState: 08001
Server Error: 6
I can connect to MSDE by using the IP a ping gave me,
1.2.3.4\Instance.
Username and Password must be correct, because a connection with
IP\Instance works fine for the IP looked up a second ago. So my
Question is: Why does Name-Lookup work for ping, work for pcAnywhere,
but not for sql server?
I wonder if someone can give a hint on that on... looking Google
Groups and Knowledge base for the last 2 hours wasn't helpful...
Thanks!Sorry, but since nobody answered, and I really need a little help
here, I *bumped* this one up again.

> Hello!
> I have noticed a strange behaviour of Enterprise Manager (or every
> program to connect to SQL Server; as in Visual Studio, Query Analyser
> and ODBC-Connection Manager), which I cannot get sorted out.
> I try to connect to an MSDE-Instance on a clients' Server. The Server
> has, for our Maintenance, a dial-up connection with dynamic IP and
> runs a service to keep the IP up-to-date, so we can access it by
> servername.dyndns.org.
> I can ping the server and I can connect to it in pcAnywhere (using the
> dyndns.org lookup).
> If I try to connect to the MSDE as servername.dyndns.org\Instance, I
> get an error: Server not found: Connection.Open(Connect()).
> Trying to make an ODBC-Connection gives some numbers on the error:
> SQLState: 01000
> Server Error: 11004
> followed by
> SQLState: 08001
> Server Error: 6
> I can connect to MSDE by using the IP a ping gave me,
> 1.2.3.4\Instance.
> Username and Password must be correct, because a connection with
> IP\Instance works fine for the IP looked up a second ago. So my
> Question is: Why does Name-Lookup work for ping, work for pcAnywhere,
> but not for sql server?
> I wonder if someone can give a hint on that on... looking Google
> Groups and Knowledge base for the last 2 hours wasn't helpful...
> Thanks!