I have an IBM Thinkpad , not the t40 though. I can't remembe the model right now, but my hd had a password, and luckily the "seller" of the laptop remembered it. But other then that, before he did, i did vast research on thinkpad passwords. For the poweron passwords i believe u just take out the cmos battery. No need to open the laptop , atleast in my model. Where the battery is, take the battery out, and theres should be a place somewhere aroudn there with a tiny screw or something, just short the jumpers. U'll figure it out after u take out the battery, its not too hard. It should taket out the poweron. But thats only poweron, if its a hard drive, u gotta replace it, and if its a supervisor password, u are just as (filtered).
Take a look here
http://www-3.ibm.com/pc/support/site.wss/MIGR-39298.htmlHope that helps.