Difficulty creating admin user on WordPress install

Hey folks.

Here’s my situation: I’ve got an old website, hosted somewhere that’s not DreamHost, at example.com. I want to create a new WordPress site at DreamHost (and if possible, I’d really like to keep example.com pointing to the old site until the new one has been fleshed out with content and themes, etc.).

I created a domain through the DreamHost control panel, at example.com. I then went to the one-click install menu and started a WordPress installation. The automatic email with more instructions, however, told me to go to example.com/wp-admin/install.php, but at the moment, that just gives me a 404.

What I’d like to do is:
[list=1][]finish this WordPress installation, and
]edit/work on my new WordPress site while example.com still points to the old site.[/list]
Can I do both? If so, how? If not, then the priority question is, how do I finish the WordPress installation?