James:
I'm not addressing the Informix part of your post, but as far as SAMBA is concerned, it will make the Unix box look like any other Windows server. Once SAMBA is setup on the Unix system (you don't have to do anything with the clients if their running Windows) you can map the resources on the Unix box same as you would in a Windows network.
Hope that helps an itsy bitsy bit.
Scott
Scott Ramey
BDS Software