Hi Shane,
I have recently done what you are trying to achieve, except our BASIS team managed the server side stuff so I probably can't help that much with those steps.
If I were you I would try a few things:
1. Make sure that the MYSAPSSO2 cookie is being passed in the HTTP request. You can do this by either opening the NWBC for HTML and using the developer tools (Chrome, Firefox or IE) or using a proxy like Fiddler2 to see the traffic.
2. Once you are sure that the logon ticket (MYSAPSSO2) is being sent, then check the server logs to see if you can see any problems on the server side. There must be a way to set the trace level to high on the server so that you can see the request coming in and the ticket being processed.
Sorry I can't help more - I will ask our BASIS team and see if they can share any insights.
Thanks,
Simon