kernel-source? (compiling 3c509.c on RedHat 7.0 kernel 2.4.2-2)

I am new to Linux.

I am trying to compile the driver 3c509 on RedHat 7.0 distrubution, kerne=
l 2.4.2-2,=20
but I get the following error message from modversions.h:

Modules should never use kernelheaders system headers, but headers from=20
appropriate kernel source

What is a appropriate kernel source? Should I include, create, download s=
ome file?

Please help me with this problem, I am going mad!

Thank you!
Anders Persson
Norrk=F6ping, Sweden