If found that 192 is the sweet spot (for a gamer) of Win98, I can't imagine ME being different. When I went from 128 to 192 load times for levels went down, rebuilding the geometry of my own custom created levels went down, but I didn't get a framerate increase or anything. The only time I saw a FPS increase was when I went from CAS3 to CAS2 Ram and that was only in Unreal engine games. I would say that 192 is good, unless you can get 64 megs for dirt cheap.
Sd- I have heard that as an OS windows will only use 128megs, but other programs (games, word proc, graphics editing) will use it all depending on how they manage memory usage. Probably an Urban legend. A few years ago when a 128 megs was a lot for a consumer, the legend was that windows would only use 64 megs and other programs would use any other ram in there. Go figure. Take those "it will only use x megs or ram" with a grain of salt. Until someone takes apart the windows kernal and shows me, I won't totally believe it.