Multiple blogs if I already installed as a single?

I have a WordPress blog already up and running on my server. Now I want to add another blog for a fmaily member.

Do I have to resinstall? I tried just upoloading all the install files ina seperate directory and running wp-config, but no luck.

I changed the wp_ line in wp-config.php to vt_ for him. Do I have to rename all the files?

Any help is MOST welcome. Thanks! ??