CentOS 5 :: Display Script That Users Can SSH In And Invoke?

I'm trying to do a little bit of setup on our new server and could use a hand.I'm working on creating a simple display script that our users can SSH in and invoke, here is what I'm attempting to do.

Requirements.

1. Must run X over ssh on Mac OS X 10.5 or greater

2. Must work in the office, or on the road

Implementation:
1. Set up the system to auth against LDAP (Open Directory)

2. Create a script on the PATH that checks which displays are available, and launches Xephyr for the first available one.

3. Create a client script that performs the SSH and Xephyr command so that users can simply click the script to start an X session.

I have 1 set up, but I'm having issues with 2 and hence 3. For instance, I can start XNest with the following commands.Start my SSH session

ssh ninet@10.0.1.50 -X

Load XNest
Xnest :1 -ac -geometry 1024x768 -once -query localhost