Hello,
I assume you've been trying to install the latest nightly?
It shouldn't, but the admin registration script encodes the email address; you'll never receive the email.
In order to access the dashboard, you'll need to manually edit the database. This assumes you have access to it, via phpMyAdmin for example.
In the wp_users database (you may have chosen a different prefix than wp_), you'll find the admin user is there.
What you need to do is replace the password field in that entry:
1. Create an MD5 string from the password you wish to use (that can be created on this page or using any MD5 encoder script)
2. Paste the resulting MD5 hash into the password field
3. Save the database entry
You can now log into WPMU and access the dashboard.