GerBot - 6:03 pm on Feb 13, 2006 (gmt 0) Sounds like you have two questions. Your other question is about increasing your rank through various IPs/ISPs.
Given my problems I'm probably not the one to be advising anyone but.....
Most of the items I've assumed are causing my problems should not effect you if you are using your webhost's nameservers and staying in the same regional SERPs. You should just be able to follow the normal server migration practice outlined by Matt Cutts on his blog. Just make sure when the website has switched servers you don't leave a htaccess files on you old server's IP as I think this may have been my downfall.
This is a whole new world to get into but basically interlinking your websites will not 'hurt' you if they are on the same server, but they will not give you the link 'vote' normally associated with an independent link vote. After this you get into questions about C class IPs, different whois info and ISPs. You'll want to ask this question in a different thread and also read through this form as it is a large area of discussion and you'll get many different theories.
Sounds like you have two questions.
Your other question is about increasing your rank through various IPs/ISPs.