I'm not sure where this all fits into the ScummVM picture, especially since COMI is 100% compatible with ScummVM and that Grim is playable until a certain point using Residual...
However, I wanted to point out that the installers for both games do not work at all under Vista 64bit. I have downloaded Vista x64 RC2, and tried to launch several games in order to see if the switch is worthwile. When I try to install COMI using the LEC launcher, I first get this error (click for bigger image, image is hosted on pix.nofrag.com) :

So I navigate to the install folder, try to run the installshield Setup application, and there I'm greeted with the following:

Same thing is valid for Grim Fandango...
I don't know if it's useful to bring this up to the guys at LucasArts, maybe they don't even know about these games anymore, but it saddens me to see that it's impossible to even install a game when the OS or the launcher decides that this 32bit app is incompatible! Welcome to Trusted Computing...