Andreas,
In a Windows systems usually under C:\windows\system32\drivers\etc, the "hosts" file should have an entry:
192.168.0.53 myname.dyndns.org
Note that this is only for those systems on your internal network so they can find your Moodle server. On my home office network, I have two Windows systems, one Windows server with Moodle and one Linux server with Moodle inside the router. The two Windows systems have an entry in their "hosts" files to find the Moodle servers.
Hope this helps...
Cheers,
Bob