This is a documentation of my first attempt to install WordPress MU. Since others will certainly face this situation I thought it would be helpful to tell my story.
The first steps are very straightforward. It's only until you begin the installation that you'll most likely encounter problems. I should note that I'm coming at this from a background in having installed the single-blog version of WordPress many times before with no problems however in hindsight, my assumptions about WordPress have led to problems installing WordPress MU due to the differences between it and the single-blog version of WordPress which I only later discovered - so don't assume.
Briefly, the differences I encountered related to database design and configuration. Another issue I had was due to my local (WAMP) development environment which produced the following error message right from the start:
"Installing to http://localhost/ is not supported. Please use http://localhost.localdomain/ instead."
I didn't know what http://localhost.localdomain/ was and clicking the link they gave me didn't do anything except hang my computer. After some quick Googling, I discovered that using 127.0.0.1 (instead of 'localhost') remedied my problem. If this doesn't work for you then... you're on your own.
Let's get started...
Step 1: Download WordPress MU
Step 2: Extract all files into desired folder
Step 3: Read README.txt
Step 4: Enable mod-rewrite
For Apache on my machine, mod-rewrite is not enabled by default. Instructions for enabling it are well documented online.
Step 5: Create Database (without any tables)
In PHPMyAdmin this task is fairly simple (assuming you're working local or have root access). (Creating a database is one of the things that the installer cannot do for you.)
Step 6: Begin installation
Point your browser to whichever directory you extracted your files to (ex: http://www.yourdomain.com/blogs/). The index.php file will load automatically and either throw more error messages at you or present you with a friendly "Installing WordPress µ" screen. If you have reached the latter, you will need to make some choices and fill in some forms before proceeding. An important choice will be to decide on using sub-domains or sub-directories. This is another topic which has been well documented so I won't go into detail. I chose to use subdirectories so this article may be more applicable if you choose to do the same.
Finish off this first step by entering your DB info and other details and clicking 'submit'.
Step 7: Fail installation and start over
This isn't actually part of the process but I failed here so I want to document it. Basically my install just hung. After I clicked submit, I was presented with some waiting and then a page which said "Wordpress µ" or something and when I refreshed the screen, I see "My Blog" with an 'Error 404 - Not Found' message. Furthermore, my login page is not styled and I never received a login/password which leads me to believe something didn't finish during the install process. My only choice was to delete the files and database and re-try.
extracting files again...
Ok - Round 2...
Fortunately this time my computer did not hang. If your installation was successful, you will see a screen with the message 'Installation Finished! Congratulations! Your WordPress µ site has been configured."
You can also point your browser to the folder into which you extracted your files (ex: http://www.yourdomain.com/blog/) and if you see your blog title + 'Just another weblog' then you're good to go.
Step 8: Log in and make sure everything looks good
Traditionally you would log in to your WordPress Admin control panel via http://www.yourdomain.com/blog/wp-admin/ however when I do this, I get bounced to http://127.0.0.1/wp-admin/ which just shows 'Not Found'. With WPMU you need to go to http://www.yourdomain.com/blog/wp-login.php and enter the username/password which was given to you on the installation completion screen.
If you can successfully log in then you're done! From here you can start posting, try adding new accounts, change your theme, etc. If you encounter any problems I haven't addressed here, please post them and we'll see if we can't find a solution.
BTW, the website I used for this quick tutorial (www.JealousBrother.com) is a site which I built that just launched a couple weeks ago. It's a rivalry based interactive social networking site. We've installed MU and are still figuring on whether to fully integrate it with the site (every new user gets a blog automatically) or just allow new users to 'activate' their blog when they want it.
If anyone has any experience doing this / suggestions / advice / etc. I'm very open to hearing what you've got.