Dear Don,

It is human that people resist any changes. I have gone through this pain when i was introducing the Access database in July 2010. Some of the program managers were so used to Excel that they didn't want to change at all. But i can assure you, there is always a way out. But it will involve a lot of sacrifice in terms of time and patience from your side.
In addition to what Richard mentioned, may be you could find out in more details what else they do with the data especially in terms of analysis. i am sure you have done this already. or which reports (read indicators) they submit to their donors/clients. If any summary/indicator can be generated from the Access Db, include it. Essentially, provide more functionality than what they could ever get in Excel within the same time interval. Eventually, they will find the Accesss database irresistable to use.
Also, use every opportunity to train the users. I have found this very useful.
Ask questions like...What else would you like this database to do for you? and of course, you will have to find a way of making the DB simpler and simpler to use everyday.
Bottom line, listen to their feedback/concerns and fix anything they may not like even if it is changing the color of a form. Because at the end of the day, they are the ones who will use (read pay) the DB not you.

I can tell you the truth, the manager who resisted most (started using the database three months later), is the one who is now helping me to write the user manual!This could probably give you an idea of how attitudes towards something can change.

Wishing you good luck in your project!

MICAH