I downloaded A Better Finder Attributes and got to inspect the interface. It's pretty spiffy. If the app had let me change the dates on more than 5 files in trial mode, I would have instantly spent the cash to buy it. Alas, 5 files was the limit, so I went looking elsewhere. I did find another shareware utility that would let me do more than 5 files, but I kept searching and found this neat and simple AppleScript that works fine:
The instructions for turning it into an app are included. Just drop your files on the app after you create it, enter the date and time in YYYYDDMMDDhhmm format, click "Continue" , and you're done.
A Better Finder Attribute has a nice interface, and can do more than change creation dates. If I ever need all the functions it provides, I won't hesitate to buy it. But for just changing the creation dates on a dozen or so files, the script linked above works fine.