>Any way to take control of social networks like Facebook, Twitter, LinkedIn... ?

You wish...

>By taking control I mean primarily posting messages from VFP to those social networks.

Ah, that. Instantiate IE aka browser object, start fiddling with the document you see. Or check to see whether these guys have some API. My neighbor's blog has some script (for wordpress) which runs inside the blog (which, being WP, is built on php) and reposts the first paragraphs of blog entries, their headlines and first photos to facebook automatically. So I guess they should have an API, probably some kind of web service.