I drain and refill the pan every 3-4 months. You'll get about 2 qts out when you drain the pan (I think it holds something like 10 qts total). Unless you have a transmission problem, I wouldn't change the filter. I changed the filter on my former LS at 250k+ miles, and the filter was spotless, as was the one in my '99 when I did a transmission repair at 180k miles. I just ordered 12 quarts of T-IV from Park Place for $59 shipped.
Whoa... you're driving a Lexus, not a Chrysler! Every 3-4 months sounds insane! :P :D
In the owners manual I have from my '95, the maintenance charts are on pages 184-187. If your manual doesn't have it, I can post the pages. Assuming you fall under the light service category, the 52,500 mile service is just an oil change, check the body for corrosion, check the a/c filter, and a road test.
Thanks for the info. I'll take a look, but I'm fairly certain I've looked for it many times before and it just referred me to the "maintenance booklet" that did not come with my car.