If you dont want to integrate YAF into your website, and just make it as a normal installation, the instructions for installation are supplied in the install.txt...
Because if all you want to do is install YAF to your existing database, then i think i have already answered that already...
Just modify the connectionstrings from db.config to point to your database
Lets say you wanted to connect to "database1" your connectionstrings should look something like this"
I assume you are running it on your server "localhost" and i assume your instance nam is "SQLESPRESS" (Otherwise just edit it to your instance name)
on the addname="database1" replace it with the name of your connectionstring in your root web.config
and Catalog="database1 to your existing database name that you want YAF installed in
It jus me or theres not much support? (See lots of ananswered posts for weeks, "specially mine" )