OK, so you already have an existing SMTP on that box then. Makes a big difference I guess.
For that, make sure you have a valid user specified in your php.ini file. I (unfortunately) had the pleasure of setting up a site on IIS a couple weeks ago, and that was one of the things I remember having to correct.
As a note, however, by default WP and WPMU use sendmail and not SMTP. I ended up needing the plugin anyway to get mail to work on that IIS box, but that may be because the SMTP server required a username and password for authentication.
Onto the password deal.
Like I said, do you have a working version of WP on this same box? Not your MU install, plain old WP. The newer, the better.
Since MU is built from WP, the password function is the same.
So, you can open up the WP (standard) DB, get into the user table, and grab the hash from one of the users (like admin) where you already know what the password is.
Then, you can open up your WPMU db, get into the users table, and edit the admin account. Paste the password hash from the standard WP db you copied, into the MU's user field to replace the one that MU generated and "sent" to you.
Now, you have a new hash in there, that you already know the password for.
What you're doing is taking a hash from a standard WP install, sticking it into MU, so you already know the password to log in with.
Hopefully that makes more sense.
If you don't have a local version of WP running on the same box, you can install one temporarily to make a hash.
It's a little bit of a hassle, but at least you can get logged in.