WordPress MU

Hi,
I finished my global categories mod and also created a tag / category cloud that displays all categories. Now I want to display them with search engine friendly urls.

I tell the global categories mod via $_GET what posts of which category it should display. My first problem is that I can't get the rewrite to work.

This is the first standard part of my .htaccess

RewriteEngine On
RewriteBase /

# Rewrite http://www.domain.com to domain.com
RewriteCond %{HTTP_HOST} ^www\.(.*)
RewriteRule ^(.*) http://%1/$1 [R,L]

#uploaded files
RewriteRule ^(.*)?/?files/(.*) wp-content/blogs.php?file=$2 [L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-.*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

#and here comes the rewrite rule that doesn't work
RewriteRule ^categories/(.*)$ categories/?c=$1 [L]

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Even if I could rewrite the url like this how could I get $_GET to work after the url is rewritten?

Any help would be great!

deltakid, while I can't help you with the .htaccess rewrite issues, I (and many, many, others) would be (eternally) grateful if you would be willing to publish your mod once it's done?