confusing problems with /usr/include/linux when comipling modules

[ctest@neural.dlsemc.com]

i'm trying to compile userlink-source on the latest "stable" distribution.  it
complains that /usr/include/linux/modversions.h dosn't exist (which it dosn't),
and if i switch /usr/include/linux to be a link to
/usr/src/kernel-headers-2.2.17, it just chokes during compile with compile
errors.

i've heard that linking /usr/include/linux to /usr/src/kernel*/include/linux is
evil before, and really haven't appreciated the reason why.

What is the approperate solution to this situation?  (for userlink-source, but
for modules in general, as well...  i've had this situation occur before).

Thanks,
        Corey