Thanks for both of your helpful and illuminating responses.
I've made it a bit further reading through the main editor documentation PDF, and just finished reading the section on graphic sheets. I even followed his suggestion of looking at the graphics files in ResEdit — wow! It's great to be able to see all the graphics in the game! I'm amazed at the number and variety of them — looks like I won't have to create any graphics of my own for my scenario, which is very good since I have no artistic talent.
I also dug around in the stealth.cmg, valley.cmg, etc. files in ResEdit, and sure enough, there were the pictures for Jaen and Stalker, and that delicious apple pie. Boy, that pie looks good! I also took a look at the Nethergate graphics files. It's nice just to look at all the items and terrains, if nothing else. I see that there are quite a few Geneforge graphics in Blades, apart from those pesky mines.
Yes, Andrew Hunter's work on these games is great — I've written him two or three times and he's been able to give me picture files of the startup screens from various Spiderweb games. They make for excellent desktop pictures. Phil Foglio's art, especially on the character statistics screen, is also excellent, and I always look forward to seeing his drawings for various skills with each game.
EDIT: Sorry about the double-post. I have no idea how that happened!