100% usage on your CPU shouldn't be causing overheating (same applies to GPUs) - is there any dust built up in/around your laptop's fans/vents? Maybe the cooling isn't adequate for the system, something that seems to be common with laptops.
I think it is beside the point whether there is enough cooling or not, I was mostly interested in that is this really how these games are supposed to run (apparently yes?), and maybe also why these games want to use up all CPU cycles they can find. Lazy programming?
I had those overheating issues mainly just when my old T400 laptop was sitting on a dock station, maybe that somehow blocks the ventilation a bit. When I use it separately, it runs cooler, also with BG2. When I tried BG2 e.g. on my newer ASUS G75VW laptop (where one core was locked to 50%), it ran quite cool.
It just feels somewhat... stupid, that the game tries to run at 100% power on anything it can find. Maybe I'd like to play the game on battery power, in which case it excessively uses too much power, when it could clearly do with much less? Or, I wouldn't like listening to a fan speeding up to full speed just for one 13 years old game? Just as two examples. Fortunately with laptops you can force the system to use less CPU power, when I set the max CPU speed to low level on my T400, it was still plenty for BG2, ie. it ran the same at max settings as with unlimited CPU speed.
I've seen quite a lot of older games/programs running a core at 100%, I think they were probably intended to do so - as you said, it's just grabbing any free cycles it can find.
EDIT: Running Arcanum in the background at the moment (don't have any IE games installed at the moment), it seems to be using most of a core and my CPU has reached a maximum temperature of 59°C.
I tried running a couple of other games too on that same T400 ("The Wheel of Time" and "Diablo 2: LoD", from about the same era or earlier than BG2 + ToD), and they ran much more sanely: first of all they used both cores, and the CPU usage (on either core) was not locked to any specific value, but it varied all the time as I was playing. E.g. in menus CPU usage was much lower than during the busiest gameplay; makes sense, huh?
In comparison, BG2 seems a bit silly how it locks itself to 100% usage as soon as I run it, during intro videos, static menus and gameplay.
But enough of that, I just have to deal with it I guess. I guess I wouldn't want to play Baldur's Gate 2 in Thailand in a +35 Celsius room without air con. :)