Anyway, rather than wiping my machine (since I'm 99.9% sure that was the issue) here's the workraround I used - apologies if this is duplicated elsewhere.
1) Fully uninstall MJ from your machine (http://uninstallmagicjack.com/)
2) Create a user account (like you would for the 'as a service' approach)
3) Setup MJ under this users profile and make sure it works.
4) Set windows to automatically log the user in when the machine starts(http://support.microsoft.com/kb/315231)
5) There is no step # 5
I hope this is useful to someone!
...Now on to the hacks forum to see what else I can try with MJ!
AftrBrnr