None of these issues is a problem; the methods for implementing Exch 5.5 on win2k are well documented.
- Recommend not to use a DC as an exch server.
- Start the install as normal and you will be prompted that this software is not compatible, continue past this message and complete install.
- Reboot and then apply SP3 as this is what provides the win2k compatability.
- Check that the LDAP ports are not in conflict by looking at the services that are running, checking the event log for errors and running NETSTAT -A from the command line to list open ports (check MS KB) for more details.
- Have a beer
- I would not implement sp4 unless you have a specific problem to solve as sp3 is very stable, sp4 has issues (also well documented)