I want a workflow that, when an entry is created in List A, will generate one entry in List B for each entry in List C. Is this possible? If so, how?
Create a workflow and associate with list A. whenever a new entry is added to list a this workflow is kicked of
On this event from the Context find list C and get all list.Items then run foreach on each list item and insert one entry in List B
tell me if this works for you
You can't use foreach in workflows built with Sharepoint Designer (as far as I know). To do what you require would involve developing a custom workflow in Visual Studio. I've had to go down this route myself recently and it wasn't as bad as I expected.
There are some great walkthrough videos of this process at Robert Shelton's blog which helped me to get started.
If your MOSS 2007 development environment is 64-bit (like mine is), then you may well run into problems trying to create and debug workflows with Visual Studio 2008. In which case I would recommend WSPBuilder to help you package up your workflows for easy deployment into Sharepoint. There is a good post here on using WSP Builder
Hope this helps.