My ISP just installed DNN, but I can't find where I'm supposed to go to access the administrative side (or much of anything, for that matter).

I've asked them (a local ISP) and am awaiting a response from them, too. So it's possible they customized the installation. It was a slightly function installation, perhaps, because I wanted DNN in place for only one site (initially) on our web server. So it was not installed at the root of the web server to manage all our sites.

All the tutorials don't have anything explicit to say about a starting page. They all just show some default initial page that looks the same, complete with login buttons et al. But I have no GettingStarted.aspx, or login.aspx, or anything.

I can tell that DNN is installed, because all the 404 error pages are designed and have DNN's colors, rather than the default browser 404 page.