Don't know what went wrong, but my initial question didn't get posted, so here it is:

I found out how to get the game itself to run at the modern 1920x1080p resolution, along with all the other Splinter Cell games I have. However, the cutscenes in the game still run at a much lower 4:3 resolution. It's not a major annoyance, but I would still like to know if I can get the cutscenes to run at 1080p as well, considering I managed to do the same for all the subsequent Splinter Cell titles.