Changing permissions on public_html and wp-content plus deleting .htaccess
Taken from:The WordPress MU Manual
Now you’ve uploaded WordPress MU your next step is to change the permissions on your public_html and wp-content directories plus delete .htaccess as follows:
1. Double click on top folder with the dots following it (clicking that takes you back up a folder level) this closes your public_html folder and takes you up one level.
2. Now right click on your public_html folder and select file permissions.
3. Change numeric value to 777 and then click OK.
4. Double click on your public_html folder to open up the folder and then right click on your wp_content folder and select file permissions.
5. Change numeric value to 777 and then click OK.
6. Delete the .htaccess file
Next up: We’ll be looking at setting up sub-domain or sub-directory, database connection details and site email address and resetting permissions on your public_html and wp-content directories