>I'm running into another problem, though, which is that Excel
> won't quit.

Take a look at http://support.microsoft.com/?kbid=317109 This explains the stuff that Vlad posted to release the COM object


> It would appear that ASP.Net is not conducive to automation,

You've got that right.


> but I can't imagine I'm the only one generating
> Excel spreadsheets in ASP.Net!

Look around on the web and you'll find that there is plenty of people trying to do what you are trying to do and they all run into the same problems :)