Service account still doesn't work

[Erwin@ODS]

This is a follow up of my previous post "Service Account replaced by IUSR"

I'm still having problems with my app (see previous post).
After some testing I have discovered that the Web app can create a
directory when
- the parent directory has the service account in its DACL (but it won't
work when only the security group to which the account belongs is added
to the DACL)
- the path is in "Windows notation", e.g. "D:\test" but not in UNC
("\\MYSERVER\d$\test")

So, me thinks that it has something to do with network credentials. I've
found this snippet from a MSDN article :

"Note that you cannot have multiple Web applications with the same host
name if you want them to have multiple identities and to use Kerberos
authentication. This is an HTTP limitation, not a Kerberos limitation.
The workaround is to have multiple Domain Name System (DNS) names for
the same host, and then start the URLs for each Web application with a
different DNS name. For example, you would use http://app1 and
http://app2 instead of http://site/app1 and http://site/app2."

I don't have much experience in DNS, and I wouldn't know how to do that.

Can anyone someone point me in the right direction ?