The PTR record is used for reverse-DNS lookups, i.e. looking up a hostname from an IP address. If you want to be able to type in
www.mydomain.org and have it resolve to the IP address of your RedHat 9 box, then you need to have an A record in the Forward DNS Lookup Zone in Windows DNS. Once you have an A record pointing to the IP address of your RedHat box, your users will be able to access it via the FQDN.
Hope that helps,
Greg