Another approach I think of is by using the Strataframe native Connection Wizard but I don't figure out how to customize it to just populate the names of the companies available to connect. I was studying in deep the logic in the Small Business Accounting to recreate the company switching scenario. Any help be accepted.
Guillermo,
I think that you are trying to make things a little too compicated. First, you do not have to SF login form if you do not want to. You have complete control and access of the login mechanisms of the SF Role-Based Security. Secondly, you do you have to use the config file or the connection string wizard. We use neither of these in our medical software and instead have taken a different approach where the connection is auto-detected through UDP (we have a server that listens for broadcasts). This approach, however, is only used when installed in a single site. We have another approach for dealing with multiple companies logging in. We actually manipulate this at the login screen. We have a combo that allows the end-user to choose which division or company which then in turns determines how the connection string will be pulled.
StrataFrame has the ability to work in virtually any scenerio in this case, it is more a function of how you choose to design your application. I hope that maybe some of these ideas may give you an idea of an approach you may take with your application. 