Multiple blogs

I’m trying to create multiple blogs on the same server. Got one up and running which is good. However, when I try to create another blog I get the following ehen I try to install.
“wp-config-php already installed” or “need wp-config-php info” which was furnished. Also when I go to my SQL management it show no content in the data base. It appears since I already have WordPress installed on the server I can’t install another and according to the wp instructions I should be able to. I did change the $table pefix.
Can anyone help?
Tom