I'm thinking of moving my wordpress blog over to squarespace, but i'm concerned about the effect it could have on my SEO/SERP. Squarespace has the ability to import my entire wordpress db, but i'm wondering if the change google would see in the pages, would affect my SERP desite all the keywords etc being the same?
It's definately possible. As long as the internal links and the code structures don't change though, you should be fine.
Google has a strange love affair with Wordpress. If they heavily favor the linking structure and SEO factors that go into the Wordpress coding it "may" have an effect. However, ff the Squarespace software imports an exact clone of your WP blog then I don't see why it should affect it any.
Google has no love affair with WordPress whatsoever. It's just that WordPress is well-optimized for the search engines right out of the box (despite having some issues).
You need to move the content first and then change the nameservers. Only in this case you will have SEO efforst saved