To have "usefull" backlinks, is it enough if I link from a different IP or I neeed to link from different IP class? Only someone who really has the proof from experience, answer. I'm buying a hosting and I want to have two sites in different IPs or IP classes, now I'm not sure what do I need.
Different IP's is best. But setting up a blog farm on different IP addresses is a waste of time...if that's what you are thinking. I would highly recommend you review my SEO book. It clearly give you an idea of best practices and how to automate the backlink process.
This smells a lot like a spam network. Any link you can build on your own small, new website to your small, new website will be worth nothing compared to proper link building.
Yeah I agree. Don't waste your time trying to build a network of cross linked websites. It may have short term gains, but in time the search engines will see what is going on and ban you. It's not worth putting in the effort with that much risk involved. Instead build one quality website and spend that time getting good back links.