Don't know about the headers, but my software modum worked out of the box with Ubuntu 5.04... maybe you don't need to build it at all?
Its worth a shot.
I just got my Unbuntu cd's in the mail, and I have a question before I intall it. Does the cd (5.10) have the kernel sources or at the very least the headers on it. They are listed in the package list website as "Universe"
I am asking because my computer has one of those software modems and the kernel headers are needed to build the module.

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