Without knowing the name I don't think you are going to be lucky. Almost 10 years later and much of these old software titles have moved on or disappeared.

I Googled Posture Coach and got no hits at all for this software. But there is Posture software available if you Google that, Posture software.

For example, for Mac users I found this;
http://www.soundplusdesign.com/?p=3548

And for Windows users, I got this;
http://www.postureminder.co.uk/

Hopefully you will find something suitable for you. Good luck.

Mark