I have a web hosted on shared IP, I read it might affect my ranking if someone sharing the IP get blacklisted etc.
The question is: will switching to a dedicated IP AFTER the site is ALREADY on google results help? (It's on the bottom now coz I didn't do any SEO yet)
(I heard that there is some sort of "google ban" which can not be undone?)
I have switched IP addresses without SEO problems many times. Here is a check list to help you:
1) Leave your old server running
2) Set up a new server with identical content and urls.
3) Change DNS to point to the new server
4) Wait several days (or until DNS caches all expire)
5) Dismantle the old server.
Changing your domain name can be more problematic, but changing IP address isn't a big deal.
Here are a couple of threads from webmasterworld.com about changing IP addresses and the impact on search referrals from Google:
Any problem with changing IP address too often? http://www.webmasterworld.com/google/4275531.htm
Site IP address change / will it effect ranking? http://www.webmasterworld.com/google/3560063.htm