WordPress MU

Hello, Is it possible to install wpmu in the root directory, while having wp setup that root points to the wp blog?
Say, I have hxxp://domain.com/wpblog
index.php is in hxxp://domain.com and has require('./wpblog/wp-blog-header..
Now what I want to do is install wpmu in hxxp://domain.com
I tried changing the name of index.php of wpmu and work with that.
After filling in the instalation page do submit, I am taken to hxxp://domain.com/wpblog. I tried changing require to ./ but it didn't help.
What I need to do is get wpmu to work and have
blpg1.domain.com
blog2.domain.com
And at the same time not have my current domain.com/blog offline for more than few minutes.
Is this possible?
Thanking you in advance for your help

For WPMU 2.9 version coming out later this year, you can do this - because based on the info I saw, integration of existing WP site with the newer WPMU would be easier ... close to total "merge" between codebases of WP and WPMU.

In current 2.8.4a, it's possible but http://example.com/ would go to the WPMU installation in order to make it easy for your to get the subdomain installation as you want it. Ergo, you would have to move the single WP's wp-config.php and .htaccess files to the original directory /wpblog/ Two things: change wp-config.php line
require('./wordpress/wp-blog-header.php');to
require('./wp-blog-header.php');
Btw, if you do it this way, don't forget to place wpblog in "Banned Names" box if Site > Options.

Thank you very much.
I am new to wp and wpmu. Where do I put the ' weblog in "Banned Names" '

Under the Site Admin menu, look at the Options submenu. It'll be on that page.

Thank you Andrea_r.,
I tried installing wpmu to another website root to test, but I can't see any blogs I make when I try to visit the created blogs.
I made the below changes:
1. Make sure a line like the following appears in your httpd.conf
LoadModule rewrite_module /usr/lib/apache2/modules/mod_rewrite.so
(mine is in different dir (cpanel configuration), but added it as the onces I have stated.

2. In the <Directory> directive of your virtual host, look for this
line "AllowOverride None"
and change it to "AllowOverride FileInfo Options"

If I try to go to the subdomain blog, I am directed to the standard page when no content is available to a newly created website.
I believe the directoy of the subdomain-blog is empty.
Do you have any idea?

Thanks again,
John