Changing IP has less impact on SE rankings and it can be undergone through ethical promotion in short time.Now Search engines are smart enough to find the change and to find why. You don't have to worry about it.
But, before changing you need to check out the below conditions
(1) your new host should not have loads of banned ip's because of spamming and you should not end up on one of those IP's, it will effect your rankings for sure
(2) your new host should not be often down, this will definitely have an impact on your rankings, check out the up-time before you host
(3) your new host should not ban spiders to save bandwidth, this can have an effect on search engine ranking
Now Google offers domain name registration through Google’s Apps partnered with GoDaddy and eNom, Google users can spend $10 for a 1 year private domain registration. For now Google offer, .com, .net,.org, .biz, and .info and we can expect more to come on the line, so i believe you dont have to worry about "changing IP effect ranking" when you go for Google, you can get fresh IP :)
For more from Google: Will switching hosting companies or changing my IP address affect my listing in Google?