Go to http://www.xpnet.org/html/ and search for "targa". Or, for the simple solution, look at your roof and yo uwill see that it has rain gutters on the sides. Water is leaking into these because the seals have rotted. Insert sillicone rubber sealant into the rain gutter to seal it, this is the simple solution without having to take apart your roof.
I think I spent $130 for the front, rear and both sides of the targa. This is so cheap for this rubber, If I still lived in Wa. State, I'd be on the phone right after I bought a supra. Another thing to remember is that it will leak a bit sometime, every convertible, targa or sunroof I've owned has had a little leakage somewhere.