Creating a tablespace on an external server in Windows

I am having trouble using the Create_Tablespace command to create a tablespace on a mapped drive. The reason I am attempting to do this has to do with the storage capacity of my primary server, which I am reserving for our most accessed data.

System setup:
Primary server - Windows 2003 with PostgreSQL installed
Secondary server - Windows 2003 with direct connection to separate data array

I have looked through the documentation and mailing list archives and the suggestions either assume the directory is local to the machine that has PostgreSQL installed or is for linux/unix (they nicely include external mounted drives as a local directory).

What I have attempted so far:
1. Created the directories on the secondary server using Windows Explorer on my primary server. The directory where I want to create the new tablespace is empty.

2. I have tried to create the tablespace using pgAdmin III (both 1.6.x and 1.8.1). The error message is "ERROR: could not set permissions on directory "S:/postgresql/transportation": No such file or directory"

3. Read the CREATE TABLESPACE page in the online PostgreSQL manual (maybe should have done first, but it did not help anyway)

4. Created a postgres user on the secondary server and added that user as an administrator to both directories in my location path (still working with the initial install). On secondary server, have used password for both the Windows postgres user and the PostgreSQL postgres superuser in attempt to match the accounts on both servers and each setup failed.

5. Though it says not to do it, I also tried giving a location path using a UNC path and the server IP address, and as you may have guessed, that failed as well.

Other info:
- Data array is connected to secondary server as G:
- Directories on data array available on primary server through a mapped drive labeled S: (mapped to G: on secondary server)

Since I am a novice, I may just not know the correct terms when searching the mailing list archives and documentation so any help would be greatly appreciated.