The error on Mac OS X 10.5.8 has to do with libjpeg. OpenNX seems to work in 10.6, 10.7, and 10.8.
Here is an attempt to run nxssh on the command-line on 10.5.8:
macbook:~ $ /Library/OpenNX/bin/nxssh
dyld: Library not loaded: /Library/OpenNX/lib/private/libjpeg.62.dylib
Referenced from: /Library/OpenNX/bin/nxssh
Reason: no suitable image found. Did find:
/Library/OpenNX/lib/private/libjpeg.62.dylib: unknown required load command 0x80000022
Trace/BPT trap
As a result OpenNX cannot even begin to initiate a connection to any servers on Mac OS X 10.5.8.
In contrast, here is the nxssh from Nomachine's NX client on 10.5.8:
macbook:~ $ /usr/NX/bin/nxssh
usage: nxssh [-nx|-nxservermode|-nxadminmode|-nxauthonly|-nxstdinpass]
[-delkey known_hosts row] [-BE] [-1246AaCfgkMNnqsTtVvXxY]
[-b bind_address] [-c cipher_spec]
[-D [bind_address:]port] [-e escape_char] [-F configfile]
[-i identity_file] [-L [bind_address:]port:host:hostport]
[-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port]
[-P [proxy_user:proxy_password@]proxy_hostname:proxy_port]
[-R [bind_address:]port:host:hostport] [-S ctl_path]
[-w local_tun[:remote_tun]] [user@]hostname [command]
Apparently, this is a result of building libjpeg-turbo on 10.6. It's still not clear to me which exact compile flags to use, but eventually i'll figure it out.
I don't have a machine running 10.5.x anymore, so:
=> Are you willing to do some testing?
-Fritz