Well, I found that it's looking for:
if [ -f "$the_srcdir/include/linux/modversions.h" ]; then
echo "Directory \"$the_srcdir\" doesn't appear to contain kernel source."
The file modversions.h - which, I don't have - is causing the issue.
So my options are what? I had downloaded the source with apt-get, do I go out to kernel.org and find the version I need?
Or do I modify the script to look for a different file?
Plus, I'll take a look at vpnc as well.