Trying to start a newly created cluster in PostgreSQL on Windows
Aside from the upgrade recommendation (which I second btw but will not solve your current problem) your basic issue is that PostgreSQL will not run as an administrative user.  This is a security feature.

Now, if this is a desktop not on a domain model, you need to create a limited user, and run initdb as that (or assign ownership to all files under the existing second cluster to that user if it already exists which it may).  Then read the runas documentation.

Then run something like:

 runas /user:&lt;computername&gt;\postgres postgres -D C:\my\new\cluster\data\directory


So if your computer name is mycomputer, it would look like:

runas /user:mycomputer\postgres postgres -D C:\my\new\cluster\data\directory


You can also:

pg_ctl register -N postgresqlc2 -U postgres -P [password] -D C:\my\new\cluster\data\directory ....