Good question. What I meant by the "opening a door" is the plastic undercover that comes with the car - the black part with IS4WD written on it, not the filter housing. My first oil change was on my dad's RX350 so I know exactly what you mean. I had no clue on how to open it so we just kind of used a hammer to to turn it a bit so we could spin it off. But what you really need to do is use the socket wrench and that black filter housing cup thing, from this picture.
http://i257.photobucket.com/albums/hh236/m...ter_wrench2.jpg
They come in different sizes. When I bought it, I needed it for another car's "spin-on" oil filter and I expected it to work only on that car. But fortunately, it was the same size as both the IS and the RX. And the way I decided on the size was by secretly opening a new Mobil 1 filter, that fit on that car, and trying it on. I could measure it and give you the exact size of the thing if you want. Oh and it costs about 10 bucks at Walmart - where I got it.
Also, one more thing I would suggest is the extension arm for the socket wrench, like a 3-4" one. Because when you put the cup thing on with the socket wrench, it gets really hard to turn it.
So,this oil changes is also the same for a reg. RWD IS250