Here’s how I solved it: I downloaded a copy of the last version of WordPress. Even though I got similar notices that files already existed, I overwrote them and was able to proceed through the setup. Once at my dashboard, upgrading to 3.2.1 was a breeze.
Downloaded a new copy of wordpress.org, ftp’d it up to the server after deleting all the other files. On each attempt (this was in fact my third), I ran into instances of a preexisting file and the question of what to do. Previously I had overwritten with no success; this time I skipped.
I noted all the files that had the question posed except the first one and all of them were in the includes folder:
class-simplepie
formatting
functions
link-template
comment
post
Going back to my site’s wp-admin/install.php, I am welcomed with the same error on a different line. 2600 this time instead of 4218.
Any ideas what’s wrong?